#include <bits/stdc++.h>
using namespace std;

int main() {
  int N, M; cin >> N >> M;
  string Ans;
  vector<bool> Win(N);
  vector<string> S(N); for (string &T : S) cin >> T;
  for (int i = 0; i < M; i++) {
    char Hand = 'G';
    int GCP = 0;
    for (int j = 0; j < N; j++) {
      if (Win.at(j)) continue;
      if (S.at(j).at(i) == 'G') GCP |= 1;
      if (S.at(j).at(i) == 'C') GCP |= 2;
      if (S.at(j).at(i) == 'P') GCP |= 4;
    }
    if (GCP == 1) Hand = 'P';
    if (GCP == 2) Hand = 'G';
    if (GCP == 3) Hand = 'G';
    if (GCP == 4) Hand = 'C';
    if (GCP == 5) Hand = 'P';
    if (GCP == 6) Hand = 'C';
    if (GCP == 7) break;
    for (int j = 0; j < N; j++) {
      if (Hand == 'G' && S.at(j).at(i) == 'C') Win.at(j) = true;
      if (Hand == 'C' && S.at(j).at(i) == 'P') Win.at(j) = true;
      if (Hand == 'P' && S.at(j).at(i) == 'G') Win.at(j) = true;
    }
    Ans += Hand;
  }
  cout << (all_of(Win.begin(), Win.end(), [](bool ok) { return ok; }) ? Ans : "-1") << endl;
}