#include <bits/stdc++.h>
using namespace std;
int main(){
int N;
cin >> N;
int arr[N];
for (int i = 0; i < N-1; i++) {
cin >> arr[i];
}
sort(arr, arr+N-1);
for (int i = 0; i < N-1; i++) {
if (arr[i] != i+1) {
cout << i+1 << endl;
break;
}
}
}
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