#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	int n, m; cin >> n >> m;
	vector<string>s(n);
	rep(i, n)cin >> s[i];
	vector<bool>chk(n);
	string ans;
	map<char, int>gcp;
	gcp['G'] = 0;
	gcp['C'] = 1;
	gcp['P'] = 2;
	vector<char>hand = { 'G','C','P' };
	rep(i, m) {
		map<int, int>mp;
		rep(j, n) if (!chk[j]) {
			mp[gcp[s[j][i]]]++;
		}
		if (mp.size() == 3) {
			cout << -1 << endl;
			return 0;
		}
		if (mp.size() == 0) {
			ans += 'G';
			continue;
		}
		//	for (auto[k, v] : mp) {
		//		cout << k << " " << v << endl;
		//	}cout << endl;
		if (mp.size() == 1) {
			rep(i, 3) if (mp.count(i)) {
				ans += hand[(i + 2) % 3];
			}
		}
		if (mp.size() == 2) {
			rep(i, 3) if (!mp.count(i)) {
				ans += hand[(i + 1) % 3];
			}
		}
		int my = gcp[ans.back()];
		int oh = (my + 1) % 3;
		rep(j, n) {
			if (gcp[s[j][i]] == oh)chk[j] = true;
		}
		// roop
	}
	cout << ans << endl;
	return 0;
}