491A-1

#include <bits/stdc++.h>

using namespace std;

int main() {
    int a, b, c, n;
    cin >> a >> b >> c >> n;

    int n1 = a - c;
    int n2 = b - c;
    int n3 = c;
    int n4 = n - n1 - n2 - n3;

    if (n1 >= 0 && n2 >= 0 && n3 >= 0 && n4 > 0)
        cout << n4;
    else
        cout << -1;
}