#include <algorithm>
#include <iostream>
#include <map>
using namespace std;

int main() {
	const multimap<unsigned int, int> x = {{1U, 13}, {2U, 'a'}, {1U, 0}};
	auto it = x.cbegin();
	
	while(it != x.cend()) {
		auto end = x.upper_bound(it->first);
		
		cout << it->first << "\n\t";
		for_each(it, end, [](const auto& i){ cout << i.second << '\t'; });
		cout << endl;
		it = end;
	}
}