//DFS(TLEかな)
#include <iostream>
#include <algorithm>
#include <atcoder/all>
#include <set>
using namespace std;
using namespace atcoder;
using ll = long long;
//#define endl "\n";
ll N, M, chk[100009];
string S[100009];
vector<char> ans;
vector<char> te = {'G', 'C', 'P'};
set<ll> rest;

void dfs(ll pos){
  if(pos == M){
    if(rest.size() == 0){
      for(auto s: ans) cout << s;
      cout << endl;
      exit(0);
    }else{
      return;
    }
  }
  vector<ll> visited(3, true);
  for(int k = 0; k < 3; k++){
    for(auto itr = rest.begin(); itr != rest.end(); ++itr){
      if(S[*itr][pos] == te[(k + 2) % 3]){
        visited[k] = false;
      }
    }
    if(visited[k]){
      vector<ll> tmp;
      for(auto itr = rest.begin(); itr != rest.end(); ++itr){
        if(S[*itr][pos] == te[(k + 1) % 3]){
          tmp.push_back(*itr);
        }
      }
      ans.push_back(te[k]);
      for(auto p: tmp) rest.erase(p);
      dfs(pos + 1);
      for(auto p: tmp) rest.insert(p);
      ans.pop_back();
    }
  }
}

int main(){
  cin >> N >> M;
  for(int i = 0; i < N; i++){
    cin >> S[i];
    rest.insert(i);
  }
  dfs(0);
  cout << -1 << endl;
  return 0;
}