#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int main() {
    
    int N[10] = {0};
    for ( int i = 0; i < 9; i++ ) {
        int a;
        cin >> a;
        a--;
        N[a] = 1;
    }
    for ( int i = 0; i < 10; i++ ) {
        if ( !N[i] ) { cout << i+1 << endl; }
    }
    
    return 0;
}