#include<stdio.h>
int main(){
    int n;
    scanf("%d",&n);
    if(n!=1 || n<=0 ||n>10){
        print("Invalid input");
        return 0;
    }
    int arr[n-1];
    int sum=n*(n+1)/2;
    int asum=0;
    for int(i=0;i<n-1;i++){
        if(scanf("%d",&arr[i])!=1 || arr[i]<=0){
            print("Invalid input");
            return 0;
        }
        asum+=arr[i];
    }
    int num=sum-asum;
    printf("%d\n",num);
    return 0;
}