#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0);
template <typename T, typename U>
inline void amin(T &x, U y) {
  if (y < x) x = y;
}
template <typename T, typename U>
inline void amax(T &x, U y) {
  if (x < y) x = y;
}
template <typename T>
inline void write(T x) {
  int i = 20;
  char buf[21];
  buf[20] = '\n';
  do {
    buf[--i] = x % 10 + '0';
    x /= 10;
  } while (x);
  do putchar(buf[i]);
  while (buf[i++] != '\n');
}
template <typename T>
inline T readInt() {
  T n = 0, s = 1;
  char p = getchar();
  if (p == '-') s = -1;
  while ((p < '0' || p > '9') && p != EOF && p != '-') p = getchar();
  if (p == '-') s = -1, p = getchar();
  while (p >= '0' && p <= '9') {
    n = (n << 3) + (n << 1) + (p - '0');
    p = getchar();
  }
  return n * s;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n, k, *h, smin, c;
  n = readInt<long long int>();
  h = (long long int *)malloc(n * sizeof(long long int));
  k = readInt<long long int>();
  for (int i = 0; i < n; i += 1) h[i] = readInt<long long int>();
  sort(h, h + n);
  reverse(h, h + n);
  if (h[0] == h[n - 1]) {
    write(0);
    return 0;
  }
  smin = 1;
  c = 0;
  for (int i = 0; i < n - 1; i += 1) {
    for (int j = h[i]; j >= h[i + 1] + 1; j -= 1) {
      if (c + i + 1 > k) {
        smin++;
        c = i + 1;
      } else
        c += i + 1;
    }
  }
  write(smin);
  return 0;
}
