#include <iostream>
#include <vector>

using namespace std;
int main()
{
	vector<int> N(10);
	for(int i=0;i<9;++i){
		int num;
		cin >> num;
		N[num-1] = 1;
	}
	for(int i=0;i<10;++i){
		if(N[i] == 0){
			std::cout << i+1 << std::endl;
		}
	}
	return 0;
}