#!/usr/bin/env python3

with open('input.txt', 'r') as f:
    package_ids = [x.strip() for x in f.readlines()]

# print(package_ids)

def find_close(package_ids):
    for i, el_1 in enumerate(package_ids[:len(package_ids)]):
        for el_2 in package_ids[i + 1:]:
            diffs = 0
            for j, char_1 in enumerate(el_1):
                char_2 = el_2[j]
                if char_1 != char_2:
                    diffs += 1
            if diffs == 1:
                return el_1, el_2

def remove_differing(id_1, id_2):
    for i, char_1 in enumerate(id_1):
        char_2 = id_2[i]
        if char_1 != char_2:
            return id_1[:i] + id_1[i + 1:]

close_1, close_2 = find_close(package_ids)
common = remove_differing(close_1, close_2)

print('Close IDs:', close_1, close_2)
print('Common letters:', common)