#include <bits/stdc++.h>
using namespace std;

class VampireTree
{
	public:	int maxDistance(vector <int> num)
	{
		int sum = 0;
		int nonOne = 0;
		for(auto deg : num)
		{
			sum += deg;
			if(deg > 1)
				nonOne += 1;
		}
		if(sum != (num.size()-1) * 2)
			return -1;
		return nonOne + 1;
	}
};