#include <iostream>

using namespace std;
int main()
{
    int x;
    int a;
    int b;
    int c;
    bool flag = true;

    cin >> a >> b >> c;

    x = c + b;

    if (c <= b && c % a == 0)
    {
        cout << c / a << endl;
        flag = false;
    }
    if (x % a == 0)
    {
        cout << x / a << endl;
        flag = false;
    }
    if (flag)
        cout << -1 << endl;
}