N,M = list(map(int,input().split()))
S = [input() for _ in range(N)]

d = {"G":"P", "P":"C", "C":"G"}

win = set()
ans = []
for i in range(M):
    a = set()
    for j in range(N):
        if(j in win):continue
        a.add(S[j][i])
    
    if(len(a) == 1):
        for j in range(N):
            win.add(j)
        ans.append(d[a.pop()])
    elif(len(a) == 3):
        print(-1)
        exit()
    elif(a == set(["G","P"])):
        for j in range(N):
            if(S[j][i] == "G"):win.add(j)
        ans.append("P")
    elif(a == set(["P","C"])):
        for j in range(N):
            if(S[j][i] == "P"):win.add(j)
        ans.append("C")
    elif(a == set(["C","G"])):
        for j in range(N):
            if(S[j][i] == "C"):win.add(j)
        ans.append("G")
    elif(not a):
        ans.append("G")
    else:
        assert False

print("".join(ans) if len(win) == N else -1)