#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <string>
#include <numeric>
#include <cstring>
#include <cmath>
#include <set>
#include <queue>
#include <stack>

const int MOD = 1e9 + 7;
const int iINF = 1000000000;
const long long int llINF = 1000000000000000000;
#define rep(i,n) for(int i=0;i<(n);i++)

using namespace std;
using ll = long long int;
using P = pair<int, int>;
using edge = struct{int to; int cost;};

int main()
{
    int a[9];
    rep(i, 9) cin >> a[i];

    for(int i = 1; i <= 10; i++)
    {
        if(i != a[i - 1])
        {
            cout << i << endl;
            break;
        }
    }

    return 0;
}