#include <bits/stdc++.h>
using namespace std;
int main(){
int N;
cin >> N;
if (N < 2 || N >= 200000) {
return 0;
}
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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