491A-2

#include <bits/stdc++.h>

using namespace std;

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

    int n3 = c;
    for (int n1 = 0; n1 <= n; n1++)
        for (int n2 = 0; n2 <= n; n2++)
            for (int n4 = 1; n4 <= n; n4++)
                if (n1 + n3 == a && n2 + n3 == b && n1 + n2 + n3 + n4 == n) {
                    cout << n4;
                    return 0;
                }

    cout << -1;
}