#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef pair<int,int> P;
 
const int INF = 1e9;
const int mod = 1e9+7;
const double EPS = 1e-10;
const double PI = acos(-1.0);
 
int main()
{

    for(int i = 1; i <= 10; i++){
        int a; cin >> a;
        if(i != a){
            cout << i << endl;
            return 0;
        }
    }
}