#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  long long int s, sum = 0;
  cin >> n >> s;
  long long int* v = new long long int[n];
  for (int i = 0; i < n; i++) {
    cin >> v[i];
    sum += v[i];
  }
  if (s > sum)
    cout << -1 << endl;
  else {
    sort(v, v + n);
    if (s < (sum - v[0] * n))
      cout << v[0] << endl;
    else {
      s -= sum - v[0] * n;
      if (s % n == 0)
        cout << v[0] - s / n << endl;
      else
        cout << v[0] - (s / n) - 1 << endl;
    }
  }
}
