#include <iostream>
#include <vector>
using namespace std;
int main(void) {
	int b;
	vector<int> numbers(10, 0);
	for (int i = 0; i < 9; ++i) {
		cin >> b;
		--b;
		++numbers[b];
	}
	for (int i = 0; i < 10; ++i) {
		if (numbers[i] == 0)
			cout << i + 1 << endl;
	}
	return 0;
}