#include <stdio.h>
int main(){
    int n,sum=1,total=1;
    scanf("%d",&n);
    int arr[n];
    for(int  i=1;i<n-1;scanf("%d",&arr[n++])){
        total+=arr[i];
    }
    for(int i=1;i<n;i++){
        sum +=arr[i];
    }
    int result=sum-total;
    printf("%d",result);
    
}