#include <bits/stdc++.h>
#include <cmath>
#include <algorithm>
#include <iostream>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define COUT(num,len) cout << fixed << setprecision(len) << num;
#define iN int N; cin >> N;
#define lN  ll N; cin >> N;
#define coutY cout << "Yes" << endl;
#define coutN cout << "No" << endl;
#define arrIn(arr, start, N) for (int i = (start); i < (N); ++i) cin >> arr[i];
#define arrOut(arr, start, N) for  (int i = (start); i < (N); ++i) { cout << arr[i] <<" "; } cout << endl;
#define arrCopy(arr1,arr2, start, N) for (int i = (start); i < (N); ++i) arr2[i]= arr1[i];
void yn(bool tf) { cout << (tf ? "Yes\n" : "No\n"); }
void YN(bool tf) { cout << (tf ? "YES\n" : "NO\n"); }
string ABC="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
string abc="abcdefghijklmnopqrstuvwxyz";

//cout << fixed << setprecision(20) <<

int gcd(int a, int b){ //最大公約数
  if(a%b == 0){
    return b;
  }else{
    return gcd(b, a%b);
  }
}

int lcm(int a, int b){ //最小公倍数
  return a*b / gcd(a, b);
}


int nibun(const std::vector<int>& arr, int key, int begin, int end) {
  while (begin <= end) {
    int mid = (begin + end) / 2;
    if (arr[mid] == key) {
      return mid;
    } else if (arr[mid] < key) {
      begin = mid + 1;
    } else {
      end = mid - 1;
    }
  }
  return -1; 
}

int fabs(int a,int b){
  if(a-b>0){
    return a-b;
  }else{
    return b-a;
  }
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  ll N,M;
  cin >> N >> M;
  vector<string> S(N);
  for(ll i=0;i<N;i++){
    cin >> S[i];
  }
  string ans="";
  
  ll G,C,P,GG,CC,PP;
  vector<ll> win(N,0);
  for(ll i=0;i<M;i++){
    G=1;
    C=1;
    P=1;
    
    for(ll j=0;j<N;j++){
      if((S[j][i-1]=='G'&&ans[i-1]=='P')||(S[j][i-1]=='C'&&ans[i-1]=='G')||(S[j][i-1]=='P'&&ans[i-1]=='G')){
        win[j]=1;
      }else if(win[j]==0){
      
      if(S[j][i]=='G'){
        C=0;
      }else if(S[j][i]=='C'){
        P=0;
      }else if(S[j][i]=='P'){
        G=0;
      }
    }
    if(G==0&&C==0&&P==0){
      cout << -1 << endl;
      return 0;
    }
    
    }
    if(G==1){
      ans+='G';
    }else if(C==1){
      ans+='C';
    }else if(P==1){
      ans+='P';
    }
  }
  
  cout << ans << endl;
 
  return 0;
}