/* -*- coding: utf-8 -*-
 *
 * 481.cc: No.481 1から10 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int N = 10;

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  for (int i = 1; i <= N; i++) {
    int bi;
    cin >> bi;
    if (i != bi) {
      printf("%d\n", i);
      break;
    }
  }
  return 0;
}