// editor2
#include<stdio.h>
 int main(){
     int n;
     scanf("%d",&n);
     if(n<0){
         printf("Inavlid input");
     return 0;
         
     }
     int arr[n-1];
     int sum=0, total=0;
     for(int i=0;i<n-1;i++){
         scanf("%d",&arr[i]);
         sum+=arr[i];
     }
     total = n*(n+1)/2;
     total = n*(n+1)/2;
     missing = total -sum;
     printf("%d",missing);
     return 0;
 }