import sys


def input(): return sys.stdin.readline().rstrip('\n')


def main():
    n, m = map(int, input().split())
    s = [input() for _ in range(n)]
    alive = [True] * n
    ans = []
    for i in range(m):
        st = set([s[j][i] for j in range(n) if alive[j]])

        if len(st) == 3:
            print(-1)
            return

        if len(st) == 2:
            if 'P' not in st:
                cur = 'G'
                die = 'C'
            elif 'G' not in st:
                cur = 'C'
                die = 'P'
            elif 'C' not in st:
                cur = 'P'
                die = 'G'

        if len(st) == 1:
            if 'P' in st:
                cur = 'C'
                die = 'P'
            if 'G' in st:
                cur = 'P'
                die = 'G'
            if 'C' in st:
                cur = 'G'
                die = 'C'

        if len(st) == 0:
            cur = 'C'
            die = 'P'

        ans.append(cur)
        for j in range(n):
            if s[j][i] == die:
                alive[j] = False

    if any(alive):
        print(-1)
        return

    print(''.join(ans))


if __name__ == '__main__':
    main()