#include<stdio.h>
int main(){
    int size,result;
    scanf("%d",&size);
    int arr[size];
    for(int i =0;i<size;scanf("%d",&arr[i]));
    int arr1[10]={1,2,3,4,5,6,7,8,9,10};
    for(int j=0;j<size;j++){
        if(arr[j]!=arr1[j]){
            result=arr1[j];
            break;
        }
    }
    printf("%d",result);
}