/**
 * code generated by JHelper
 * More info: https://g...content-available-to-author-only...b.com/AlexeyDmitriev/JHelper
 * @author RiaD
 */

#include <iostream>
#include <fstream>

#include <iostream>
#include <algorithm>
#include <vector>


template <typename T>
T phi(T x) {
	T result = x;
	for (int i = 2; i * i <= x; ++i) {
		if (x % i == 0) {
			result /= i;
			result *= i - 1;
			while (x % i == 0) {
				x /= i;
			}
		}
	}
	if (x > 1) {
		result /= x;
		result *= x - 1;
	}
	return result;
}
#include <cassert>


#include <iterator>


#include <string>
#include <stdexcept>

#ifndef SPCPPL_ASSERT
	#ifdef SPCPPL_DEBUG
		#define SPCPPL_ASSERT(condition) \
		if(!(condition)) { \
			throw std::runtime_error(std::string() + #condition + " in line " + std::to_string(__LINE__) + " in " + __PRETTY_FUNCTION__); \
		}
	#else
		#define SPCPPL_ASSERT(condition)
	#endif
#endif


/**
* Support decrementing and multi-passing, but not declared bidirectional(or even forward) because
* it's reference type is not a reference.
*
* It doesn't return reference because
* 1. Anyway it'll not satisfy requirement [forward.iterators]/6
*   If a and b are both dereferenceable, then a == b if and only if *a and
*   b are bound to the same object.
* 2. It'll not work with reverse_iterator that returns operator * of temporary which is temporary for this iterator
*
* Note, reverse_iterator is not guaranteed to work  now too since it works only with bidirectional iterators,
* but it's seems to work at least on my implementation.
*
* It's not really useful anywhere except iterating anyway.
*/
template <typename T>
class IntegerIterator: public std::iterator<std::input_iterator_tag, T, std::ptrdiff_t, T*, T> {
public:
	explicit IntegerIterator(T value): value(value) {

	}

	IntegerIterator& operator++() {
		++value;
		return *this;
	}

	IntegerIterator operator++(int) {
		IntegerIterator copy = *this;
		++value;
		return copy;
	}

	IntegerIterator& operator--() {
		--value;
		return *this;
	}

	IntegerIterator operator--(int) {
		IntegerIterator copy = *this;
		--value;
		return copy;
	}

	T operator*() const {
		return value;
	}

	bool operator==(IntegerIterator rhs) const {
		return value == rhs.value;
	}

	bool operator!=(IntegerIterator rhs) const {
		return !(*this == rhs);
	}

private:
	T value;
};

template <typename T>
class IntegerRange {
public:
	IntegerRange(T begin, T end): begin_(begin), end_(end) {
		SPCPPL_ASSERT(begin <= end);
	}

	IntegerIterator<T> begin() const {
		return IntegerIterator<T>(begin_);
	}

	IntegerIterator<T> end() const {
		return IntegerIterator<T>(end_);
	}

private:
	T begin_;
	T end_;
};

template <typename T>
class ReversedIntegerRange {
	typedef std::reverse_iterator<IntegerIterator<T>> IteratorType;
public:
	ReversedIntegerRange(T begin, T end): begin_(begin), end_(end) {
		SPCPPL_ASSERT(begin >= end);
	}

	IteratorType begin() const {
		return IteratorType(IntegerIterator<T>(begin_));
	}

	IteratorType end() const {
		return IteratorType(IntegerIterator<T>(end_));
	}

private:
	T begin_;
	T end_;
};

template <typename T>
IntegerRange<T> range(T to) {
	return IntegerRange<T>(0, to);
}

template <typename T>
IntegerRange<T> range(T from, T to) {
	return IntegerRange<T>(from, to);
}

template <typename T>
IntegerRange<T> inclusiveRange(T to) {
	return IntegerRange<T>(0, to + 1);
}

template <typename T>
IntegerRange<T> inclusiveRange(T from, T to) {
	return IntegerRange<T>(from, to + 1);
}

template <typename T>
ReversedIntegerRange<T> downrange(T from) {
	return ReversedIntegerRange<T>(from, 0);
}

template <typename T>
ReversedIntegerRange<T> downrange(T from, T to) {
	return ReversedIntegerRange<T>(from, to);
}

template <typename T>
ReversedIntegerRange<T> inclusiveDownrange(T from) {
	return ReversedIntegerRange<T>(from + 1, 0);
}

template <typename T>
ReversedIntegerRange<T> inclusiveDownrange(T from, T to) {
	return ReversedIntegerRange<T>(from + 1, to);
}

#include <map>

using namespace std;

vector<int> prefix_function (string s) {
	int n = (int) s.length();
	vector<int> pi (n);
	for (int i=1; i<n; ++i) {
		int j = pi[i-1];
		while (j > 0 && s[i] != s[j])
			j = pi[j-1];
		if (s[i] == s[j])  ++j;
		pi[i] = j;
	}
	return pi;
}

class TaskF {
public:
	void solve(std::istream& in, std::ostream& out) {
		string s, t;
		in >> s >> t;
		if (s.front() != t.front()) {
			out << -1;
			return;
		}
		if (s.back() != t.back()) {
			out << -1;
			return;
		}
		int n = (int)s.size();
		int phi = ::phi(n - 1);
		vector<int> used(n);
		std::map<int, vector<int>> can;
		for (int i = 1; i < s.size() - 1; ++i) {
			if (used[i]) {
				continue;
			}
			string cur;
			string cur2;
			for (int j = i; !used[j]; j = (2 * j) % (n - 1)) {
				used[j] = true;
				cur += s[j];
				cur2 += t[j];
			}

			assert(phi % cur.size() == 0);
			//swap(cur, cur2);
			//cur += cur;
			string s = cur2 + "#" + cur + cur;

			auto pi = prefix_function(s);
			//pi.erase(pi.begin(), pi.begin() + cur.size() + cur.size());

			auto& mapa = can[cur.size()];
			if (mapa.empty()) {
				mapa.assign(cur.size(), 1);
			}


			for (int u = 0; u < cur.size(); ++u) {
				if (pi[u + 2 * cur.size()] != cur.size()) {
					mapa[u] = 0;
				}
			}

		}


		for (int i: range(phi)) {
			bool can_all = true;
			for (auto& p: can) {
				if (!p.second[i % p.first]) {
					can_all = false;
					break;
				}
			}
			if (can_all) {
				out << i;
				return;
			}

		}
		out << -1;
	}
};


int main() {
	std::ios_base::sync_with_stdio(false);
	TaskF solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
	in.tie(0);
	out << std::fixed;
	out.precision(20);
	solver.solve(in, out);
	return 0;
}