#include <bits/stdc++.h>
using namespace std;

int main() {
  int n; cin >> n;
  int sumA = 0;
  for (int i = 0; i < n; i++) {
    int a; cin >> a;
    sumA += a;
  }
  int sumB = 0;
  for (int i = 1; i <= n; i++) {
    sumB += i;
  }
  cout << abs(sumA - sumB) << endl;
}