#include <bits/stdc++.h>
using namespace std;
int mod = 1000000007;
const int inf = 1034567891;
const long long LL_INF = 1234567890123456789ll;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cout << name << " : " << arg1 << '\n';
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cout.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
template <typename T>
T GCD(T a, T b) {
  long long t;
  while (a) {
    t = a;
    a = b % a;
    b = t;
  }
  return b;
}
template <typename T>
string toString(T a) {
  return to_string(a);
}
template <typename T>
void toInt(string s, T& x) {
  stringstream str(s);
  str >> x;
}
inline int add(int x, int y) {
  x += y;
  if (x >= mod) x -= mod;
  return x;
}
inline int sub(int x, int y) {
  x -= y;
  if (x < 0) x += mod;
  return x;
}
inline int mul(int x, int y) { return (x * 1ll * y) % mod; }
inline int powr(int a, long long b) {
  int x = 1 % mod;
  while (b) {
    if (b & 1) x = mul(x, a);
    a = mul(a, a);
    b >>= 1;
  }
  return x;
}
inline int inv(int a) { return powr(a, mod - 2); }
const int N = 2e5 + 5;
int n, m;
int arr[N];
bool check(int d) {
  long long total = 0;
  int cur = 0;
  for (int i = 0; i < n; i++) {
    total += max(0, arr[i] - cur);
    if ((i + 1) % d == 0) cur++;
  }
  return (total >= m);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n >> m;
  for (int i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n, greater<int>());
  long long total = accumulate(arr, arr + n, 0ll);
  if (total < m) {
    cout << -1 << '\n';
    return 0;
  }
  int low = 1, high = n, mid, ans = -1;
  while (low <= high) {
    mid = (low + high) >> 1;
    if (check(mid)) {
      ans = mid;
      high = mid - 1;
    } else {
      low = mid + 1;
    }
  }
  cout << ans << '\n';
  return 0;
}
