#include <iostream>
#include <fstream>

using namespace std;

unsigned int solve(unsigned int *N)
{
	unsigned int K = 0;
	unsigned int k = 1;

	while(true) {
		unsigned int m = 0;
		// overflow?  I've never heard that word. :-)
		for(int j = 0; j < 8; j++) m += (N[j] ^ K);
		unsigned int n = N[8] ^ K;
		if(m == n) return K;
		if((m & k) != (n & k)) K |= k;
		k <<= 1;
	}
}

int main(void)
{
	ifstream cin("C.txt");

	int n;
	cin >> n;

	for(int i = 0; i < n; i++) {
		unsigned int N[9];
		for(int j = 0; j < 9; j++) cin >> hex >> N[j];
		cout << hex << solve(N) << endl;
	}

	return 0;
}