#include<stdio.h>
#include<stdlib.h>
int main(int argc,char*argv[]){
    if(argc<3)
    return 1;
    int n = atoi(argv[1]);
     if(n<1||n>10)
     return 0;
     int total_sum =n*(n+1)/2;
     long long input_sum=0;
     int element=atoi(argv[i]);
     for(inti=2;i<argc;i++){
         int element =atoi(argv[i]);
         if(element<=0){
             printf("Invalid Input\n");
             return 0;
     }
     input_sum+=element;
     element_count++;
     
}
if(element_count!=n-1)
return 0;
printf("%d\n",total_sum-(int)input_sum);
return 0;
}