#include <stdio.h>
int main()
{
int a[55],i,j,b,n;
scanf("%d",&n);
for (i=1; i<=n-1; i++){
scanf("%d",&a[i]);
}
if((1<=b&&b<=n)&&b!=a[i]){
printf("%d",b);
}
}
/*
#include <stdio.h>
int main()
{
int a[100],i,j,k;
for (i=1; i<=10; i++){
scanf("%d",&a[i]);
}
scanf("%d",&k);
printf("%d",a[k]);
}
*/
