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