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