#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>

#define rep(i,n) for(i=0; i<n; ++i)
#define in(a) cin >> a
#define out(a,b) cout << a << b
using namespace std;
using lint = long long;

int main(void){
    int i, j, n, m, k, cnt = 0;
    rep(i,9){
        in(j);
        if(j!=i+1){
            k=i+1;
            break;
        }
        else if(i==8)   k=10;
    }
    out(k,endl);
    
    return 0;
}