#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	vector<bool> a(11,true);
	rep(i,9){
		int b;cin >> b;
		a.at(b)=false;
	}
	rep(i,10) if(a.at(i+1)) cout << i+1 << endl;
}