#!/usr/bin/env python3

# Almost the same as thore.py, but ignore that Q behaves weirdly

letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

def before(a, b):
    return a <= b

def solve(lines):
    front = lines[0]
    sides: list[set[str]] = [set() for _ in range(16)]
    for line in lines[1:5]:
        for i, l in enumerate(line):
            sides[i].add(l)
    back = lines[-1]


    # best[c] = smallest number or rotations to sort the
    # current prefix such that it ends in c. If this is impossible, None.
    best = {front[0]: 0, back[0]:2 } | {letter: 1 for letter in sides[0] if letter != front[0]}
    for i in range(1, 16):
        new_best: dict[str, int] = {}
        for letter, delta in [(front[i], 0)] + [(side, 1) for side in sides[i]] + [(back[i], 2)]:
            vals = [turns + delta for (prev, turns) in best.items() if before(prev, letter)]
            if vals:
                if letter in new_best:
                    new_best[letter] = min(min(vals), new_best[letter])
                else:
                    new_best[letter] = min(vals)
        best = new_best
    if best:
        return(min(best.values()))
    else:
        return('impossible')

print(solve([input() for _ in range(6)]))