/*
int       %d
longlong  %lld
float     %f
double    %lf
char      %c
char[]    %s
'a'=97
'z'=122
'A'=65
'Z'=90
'0'=48
'9'=57
*/
#include <cstdio>
using namespace std;
const int N=1e7+10;
const int INF=0x3f3f3f3f;
const double pi=3.1416;
int n,x,ans;
int main(){
	scanf("%d",&n);
	for(int i=1;i<n;i++){
		scanf("%d",&x);
		ans^=x;
	}
	for(int i=1;i<=n;i++){
		ans^=i;
	}
	printf("%d",ans);
return 0;
}