#nullable enable

#region
var (_input, _iter) = (Array.Empty<string>(), 0);
T I<T>() where T : IParsable<T>
{
    while (_iter >= _input.Length) (_input, _iter) = (Console.ReadLine()!.Split(' '), 0);
    return T.Parse(_input[_iter++], null);
}
#endregion

static T[] Range<T>(int n, Func<T> F) => Enumerable.Range(0, n).Select(_ => F()).ToArray();

var n = I<int>();
var m = I<int>();
var sz = Range(n, I<string>);

var ans = new char[m].AsSpan();
ans.Fill('G');
var won = new bool[n];
for (var j = 0; j < m; j++)
{
    var hz = new int[3];
    for (var i = 0; i < n; i++)
    {
        if (won[i]) continue;
        var h = sz[i][j];
        if (h == 'G') hz[0] = 1;
        if (h == 'C') hz[1] = 1;
        if (h == 'P') hz[2] = 1;
    }
    var sum = hz.Sum();
    if (sum == 3)
    {
        Console.WriteLine(-1);
        return;
    }
    if (sum == 1)
    {
        if (hz[0] == 1) ans[j] = 'P';
        if (hz[1] == 1) ans[j] = 'G';
        if (hz[2] == 1) ans[j] = 'C';
        break;
    }
    if (sum == 2)
    {
        if (hz[0] == 0)
        {
            ans[j] = 'C';
            for (var i = 0; i < n; i++) if (sz[i][j] == 'P') won[i] = true;
        }
        if (hz[1] == 0)
        {
            ans[j] = 'P';
            for (var i = 0; i < n; i++) if (sz[i][j] == 'G') won[i] = true;
        }
        if (hz[2] == 0)
        {
            ans[j] = 'G';
            for (var i = 0; i < n; i++) if (sz[i][j] == 'C') won[i] = true;
        }
    }
}
Console.WriteLine(new string(ans));