#include<bits/stdc++.h>
#include <iostream>
#include<assert.h>
using namespace std;
//const int N = 1e5+9;
//char s[N];
int main() {
// your code goes here
int n; cin>>n;
bool watched[n+1];
for(int i = 1; i<n; i++){
watched[i] = false; //initially everything is false
}
for( int i = 1; i<n; i++){
int episode; cin>> episode;
watched [episode]= true;
}
int not_watched = -1;
for(int i = 1; i<n; i++){
if(!watched[i]){
not_watched = i;
}
}
cout << not_watched << endl;
assert(not_watched != -1);
return 0;
}
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