#include <iostream>
using namespace std;

int main()
{
	
	int K, N, F, A[1000];
	int	sum = 0;;

	cout << "粒の数: ";
	cin >> K;

	cout << "袋の数: ";
	cin >> N;
		
	cout << "家族の数: ";
	cin >> F;

	for (int i = 0; i < F; i++)
	{
		cout << i+1 << "人目の年齢: ";
		cin >> A[i];
		sum += A[i];
	}

	if (K*N >= sum)
	{
		cout << (K*N) % sum << "粒残る" << endl;
	}
	else
	{
		cout << -1 << endl;
	}

	return 0;
}