#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    int total = n * (n + 1) / 2;
    int input = 0;
    for (int i = 0; i < n - 1; ++i) {
        int x;
        cin >> x;
        input += x;
    }
    int number = total - input;
    cout << number << endl;

    return 0;
}