#include<stdio.h>

int main(])
{
  int n,sum=0,num;
  scanf("%d",&n);
  for(int i=0;i<n-1;i++)
  {
      scanf("%d",&num);
      sum+=num;
  }
  int total=n*(n+1)/2;
  printf("%d\n",total-sum);
  return 0;
}