#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
lint liters(int l, vector<int> &arr) {
  lint sum = 0;
  for (int k : arr) sum += (lint)(k - l);
  return sum;
}
int main() {
  int n, m = 1000000010;
  lint s;
  vector<int> arr;
  cin >> n >> s;
  arr.resize(n);
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
    m = min(m, arr[i]);
  }
  if (s > liters(0, arr))
    cout << -1 << endl;
  else {
    int start = 0, end = m;
    while (start < end) {
      int mid = (start + end) / 2 + 1;
      if (s <= liters(mid, arr))
        start = mid;
      else
        end = mid - 1;
    }
    cout << start << endl;
  }
  return 0;
}
