#!/usr/bin/env python
# -*- coding: utf-8 -*-

def get_repeated_int(str1, str2):
    count = 0
    for i in range(len(str1)):
        if str2[i] == str1[i]:
            count += 1
    return count


def get_repeated_str(str1, str2):
    out = ""
    for i in range(len(str1)):
        if str2[i] == str1[i]:
            out += str1[i]
    return out


if __name__ == '__main__':
    inputs = []

    with open("input.txt") as fp:
        line = fp.readline()
        while line:
            inputs.append(line.strip())
            line = fp.readline()

    max_repeated = 0
    max_ids = []

    for idx1, val1 in enumerate(inputs):
        for idx2, val2 in enumerate(inputs):
            if idx1 != idx2:
                repeated = get_repeated_int(val1, val2)
                if repeated > max_repeated:
                    max_repeated = repeated
                    max_ids.clear()
                    max_ids.append(idx1)
                    max_ids.append(idx2)

    print(get_repeated_str(inputs[max_ids[0]], inputs[max_ids[1]]))