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

#define int long long
#define vi vector<int>
#define vc vector<char>
#define vs vector<string>
#define vb vector<bool>
#define vpii vector<pair<int, int>>
#define vpic vector<pair<int, char>>
#define vpis vector<pair<int, string>>
#define pb push_back
#define pii pair<int, int>
#define rep(i, s, e) for (int i = (s); i < (e); i++)
#define all(x) x.begin(), x.end()
#define fastio ios::sync_with_stdio(false); cin.tie(0);



signed main()
{
    fastio;

    vector<int> a(9);

    int k = 1;
    int t;
    for(int i=1; i<=9; i++){
        cin>>t;
        if(t != k) break;
        k++;
    }

    cout<<k<<endl;

}