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

int main()
{
    long long int n, s = 0, ele;
    cin >> n;
    for (int i = 0; i < n - 1; i++)
    {
        cin >> ele;
        s += ele;
    }
    cout << n * (n + 1) / 2 - s;
    return 0;
}