n=int(input())
l=list(map(int,input().split()))
l1=[]
for i in range(1,n+1):
l1.append(i)
k=set(l1)-set(l)
for i in k:
print(i)#include <bits/stdc++.h>
using namespace std;
int main() {
int n;
cin >> n;
n = n;
int a[n];
for(int i=0; i<n-1; i++) {
cin >> a[i];
}
sort(a, a+n-1);
for(int i=0; i<n; i++) {
if(a[i] != (i+1)) {
cout << (i+1);
break;
}
}
return 0;
}
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