#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
    int N, M;
    cin >> N >> M;
    vector<int> Ni;
    for (int i = 0; i < N - 1; i++) {
        cin >> Ni[i];
    }
    sort(Ni.begin(), Ni.end());

    int sum = 0, ans = 0;
    for (int i = 0; i < N - 1; i++) {
        sum += Ni[i];
    }
    if (sum >= M && Ni[0] == Ni[N - 2] = M) {
        cout << 0 << endl;
    } else {
        sum = sum - Ni[0] - Ni[N - 2];
        ans = M - sum;
        if (0 <= ans <= 100) {
            cout << ans << endl;
        } else {
            cout << -1 << endl;
        }
    }

    return 0;
}

/sandbox/1/a.cpp: In function 'int main()':
/sandbox/1/a.cpp:18:14: error: lvalue required as left operand of assignment
   18 |  if(sum >= M && Ni[0]==Ni[N-2]=M){