#include <bits/stdc++.h>
using namespace std;
priority_queue<int> q;
int n, x;
int main() {
  scanf("%d", &n);
  for (register int i = 1; i < n; ++i) {
    scanf("%d", &x);
    q.push(x);
  }
  for (register int i = n; i > 0; --i) {
    x = q.top();
    if (x != i) {
      printf("%d", i);
      exit(0);
    } else
      q.pop();
  }
}
