#include<iostream>
using namespace std;
int main() {
	int B;
	int b[11];
	for (int i = 1; i <= 10; i++) {
		b[i] = 1;
	}
	for (int i = 0; i < 9; i++) {
		cin >> B;
		b[B] = 0;
	}
	for (int i = 1; i <= 10; i++) {
		if (b[i] == 1) {
			cout << i << endl;
			break;
		}
	}
	
	return 0;
}