package q5;
import java.util.*;

public class Main {
	public static HashSet<String> ban = new HashSet<>();
	public static StringBuilder sb = new StringBuilder();
	public static String h = "GCP";
	public static boolean ans = false;
	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int m = sc.nextInt();
		String[] s = new String[n];
		for(int i = 0;i < n;i++) {
			s[i] = sc.next();
		}int l = 12;
		for(int i = 0;i < n;i++) {
			StringBuilder sb = new StringBuilder();
			for(int j = 0;j < Math.min(l, m);j++) {
				for(int k = 0;k < 3;k++) {
					if(h.charAt(k) == s[i].charAt(j)) {
						ban.add(sb.toString() + h.charAt((k + 1) % 3));
						
					}
				}sb.append(s[i].charAt(j));
			}ban.add(sb.toString());
		}//System.out.println(ban);
		dfs(0,Math.min(m, l),m);
		if(!ans)System.out.print(-1);
	}public static void dfs(int l,int size,int m) {
		if(l == size) {
			
			if(!ans) {
				ans = true;
				System.out.println(sb);
				for(int i = size;i < m;i++) {
					System.out.print("G");
				}
			}return;
		}ban.add(sb.toString());
		//System.out.println(sb);
		for(int i = 0;i < 3;i++) {
			sb.append(h.charAt(i));
			if(!ban.contains(sb.toString()))dfs(l + 1,size,m);
			sb.deleteCharAt(sb.length() - 1);
		}
	}
}