#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; ++i) cin >> a[i];
  sort(a, a + n);
  int coins = 0;
  for (int i = 0; i < n; ++i) {
    for (int j = i + 1; j < n; ++j) {
      if (a[i] == a[j]) {
        ++a[j];
        ++coins;
      }
    }
  }
  cout << coins;
  return 0;
}
