#include <bits/stdc++.h>
using namespace std;

int main() {
   ios::sync_with_stdio(false);
   cin.tie(nullptr);

   // freopen("input.txt", "r", stdin);
   // freopen("output.txt", "w", stdout);
   int num;
   int ans;
   bool is_found = false;
   for(int i = 1; i <= 9; i++) {
      cin >> num;
      if(num != i && is_found == false) {
         ans = i;
         is_found = true;
      }
   }

   cout << ans << '\n';
   return 0;
}