key = open('key.txt', 'r').read()
mat = open('init.txt', 'r').read().replace('\n', '')

choices = list({c for c in key} - {c for c in mat})

newmat = ''
for c in mat:
    if not c in newmat:
        newmat += c
    else:
        repl = choices[0]
        choices.remove(repl)
        newmat += repl

open('output.txt', 'w').write('\n'.join([newmat[i:i + 5] for i in range(0, 25, 5)]))