#include <iostream>
#include <string>
#include <vector>

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];
    vector<bool> won(n, false);
    bool g, c, p;
    string ans = "";
    char beat;
    for (int i = 0; i < m; i++)
    {
        g = c = p = false;
        for (int j = 0; j < n; j++)
        {
            if (won[j])
                continue;
            if (s[j][i] == 'G')
                g = true;
            if (s[j][i] == 'C')
                c = true;
            if (s[j][i] == 'P')
                p = true;
        }
        if (g + c + p == 1)
        {
            if (g) {
                ans.push_back('P');
                beat = 'G';
            }
            if (c) {
                ans.push_back('G');
                beat = 'C';
            }
            if (p) {
                ans.push_back('C');
                beat = 'P';
            }
        }
        else if (g + c + p == 2)
        {
            if (g && c){
                ans.push_back('G');
                beat = 'C';
            }
            if (c && p) {
                ans.push_back('C');
                beat = 'P';
            }
            if (p && g) {
                ans.push_back('P');
                beat = 'G';
            }
        }
        else if (g + c + p == 3)
        {
            cout << -1 << endl;
            return 0;
        }
        else
        {
            ans.push_back('G');
            beat = 'P';
        }
        for (int j = 0; j < n; j++)
            if (s[j][i] == beat) won[j] = true;
    }
    for (int i = 0; i < n; i++) {
        if (!won[i]) {
            cout << -1 << endl;
            return 0;
        }
    }
    cout << ans << endl;
    return 0;
}