#include <bits/stdc++.h>
#define FOR(i,bg,ed) for(ll i=(bg);i<(ed);i++)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007
#define int long long
using namespace std;
typedef long long ll;
typedef vector<vector<ll>> mat;
const int INF = 1e9;



signed main()
{
    int B[10];
    
    REP(i,9) cin >> B[i];
    REP(i,9) if (B[i] != i + 1) {
        cout << i + 1 << endl;
        return 0;
    }
    cout << 10 << endl;
}