use std::collections::HashSet;
use proconio::input;
use proconio::marker::Chars;
fn main() {
    input!{
        n: usize,
        m: usize,
        s: [Chars; n]
    }
    let mut ans = vec![];
    let mut remain = vec![0; n];
    for i in 0..n {
        remain[i] = i;
    }
    for i in 0..m {
        let mut hands = HashSet::new();
        for &j in &remain {
            hands.insert(s[j][i]);
        }
        if hands.len() == 3 {
            println!("-1");
            return;
        }
        if hands.len() == 2 {
            if !hands.contains(&'G') {
                remain = remain.into_iter().filter(|&h| s[h][i] == 'C').collect();
                ans.push('C');
            }
            if !hands.contains(&'C') {
                remain = remain.into_iter().filter(|&h| s[h][i] == 'P').collect();
                ans.push('P');
            }
            if !hands.contains(&'P') {
                remain = remain.into_iter().filter(|&h| s[h][i] == 'G').collect();
                ans.push('G');
            }
        }
        if hands.len() == 1 {
            if hands.contains(&'G') { ans.push('P'); break;}
            if hands.contains(&'C') { ans.push('G'); break;}
            if hands.contains(&'P') { ans.push('C'); break;}
        }
    }
    while ans.len() < m {
        ans.push('G');
    }
    println!("{}", ans.iter().fold(String::new(), |mut acc, &c| {acc.push(c); acc}));
}