#include <bits/stdc++.h>
using namespace std;
int main()
{
    int N, M;
    cin >> N >> M;
    vector<string> S(N);
    for (int i = 0; i < N; ++i)
        cin >> S[i];
    string ans = "";
    vector<bool> used(N, true);
    for (int i = 0; i < M; ++i)
    {
        int g = 0, c = 0, p = 0, cnt = 0;
        for (int j = 0; j < N; ++j)
        {
            if (!used[j])
                continue;
            cnt++;
            if (S[j][i] == 'G')
                g++;
            else if (S[j][i] == 'C')
                c++;
            else
                p++;
        }
        if (cnt == g)
        {
            ans += "P";
            for (int j = 0; j < N; ++j)
                used[j] = false;
        }
        else if (cnt == c)
        {
            ans += "G";
            for (int j = 0; j < N; ++j)
                used[j] = false;
        }
        else if (cnt == p)
        {
            ans += "C";
            for (int j = 0; j < N; ++j)
                used[j] = false;
        }
        else if (g == 0)
        {
            ans += "C";
            for (int j = 0; j < N; ++j)
            {
                if (S[j][i] == 'P')
                    used[j] = false;
            }
        }
        else if (c == 0)
        {
            ans += "P";
            for (int j = 0; j < N; ++j)
            {
                if (S[j][i] == 'G')
                    used[j] = false;
            }
        }
        else if (p == 0)
        {
            ans += "G";
            for (int j = 0; j < N; ++j)
            {
                if (S[j][i] == 'C')
                    used[j] = false;
            }
        }
        else
            ans += "G";
    }
    bool check = true;
    for (int i = 0; i < N; ++i)
    {
        if (used[i])
            check = false;
    }
    if (check)
        cout << ans << endl;
    else
        cout << -1 << endl;
    return 0;
}