#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define co(x) cout << (x) << "\n"
#define cosp(x) cout << (x) << " "
#define ce(x) cerr << (x) << "\n"
#define cesp(x) cerr << (x) << " "
#define pb push_back
#define mp make_pair
#define Would
#define you
#define please

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);


	int A[11] = {};
	rep(i, 9) {
		int a;
		cin >> a;
		A[a] = 1;
	}

	rep1(i, 10) {
		if (A[i] == 0) {
			co(i);
			return 0;
		}
	}

	Would you please return 0;
}