#include <bits/stdc++.h>
using namespace std;
long long max(long long a, long long b) {
  if (a < b) return b;
  return a;
}
long long min(long long a, long long b) {
  if (a < b) return a;
  return b;
}
bool okay(vector<long long> &v, long long d, long long k) {
  long long sum = 0;
  priority_queue<long long, vector<long long>, greater<long long>> pq;
  for (int i = 0; i < d; i++) pq.push(0);
  for (auto x : v) {
    long long ind = pq.top();
    pq.pop();
    sum += max(0, x - ind);
    pq.push(ind + 1);
  }
  return sum >= k;
}
void solve() {
  long long n, m;
  cin >> n >> m;
  vector<long long> v(n);
  for (int i = 0; i < n; i++) cin >> v[i];
  sort(v.rbegin(), v.rend());
  long long low = 1, high = n, ans = -1;
  while (low <= high) {
    long long mid = low + (high - low) / 2;
    if (okay(v, mid, m)) {
      ans = mid;
      high = mid - 1;
    } else
      low = mid + 1;
  }
  cout << ans;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
  return 0;
}
