def win(hands):
    if len(hands) == 1:
        h = hands.pop()

        if h == "G":
            return "P"
        elif h == "C":
            return "G"
        else:
            return "C"
    else:
        l, r = sorted(hands)
        if (l, r) == ("C", "G"):
            return "G"
        elif (l, r) == ("C", "P"):
            return "C"
        else:
            return "P"


N, M = [int(s) for s in input().split()]
S = [[*input()] for _ in range(N)]
remain = {*range(N)}

answers = []


for m in range(M):
    hands = {S[r][m] for r in remain}

    if len(hands) == 3:
        print("-1")
        exit()

    if len(hands) == 0:
        answers.append("G")
        continue

    w = win(hands)
    answers.append(w)

    nremain = set()
    for r in remain:
        if S[r][m] == w:
            nremain.add(r)

    remain = nremain

print(*answers, sep="")