#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, m;
    cin >> n >> m;
    int c, q;
    cin >> c >> q;

    string t = "RGB";
    vector f(3, array<int, 2>{});
    vector a(n, vector<int>(m));
    for (int i = 0; i < n; ++i) {
        string s;
        cin >> s;
        for (int j = 0; j < m; ++j) {
            a[i][j] = t.find(s[j]);
            f[a[i][j]][(i + j) % 2] += 1;
        }
    }

    vector to(3, vector<int>(2, -1));
    if (f[0][0] + f[1][1] + f[2][1] <= q) {
        to[0][0] = 1, to[1][1] = 0, to[2][1] = 0;
    } else {
        to[0][1] = 1, to[1][0] = 0, to[2][0] = 0;
    }
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            int x = a[i][j], p = (i + j) % 2;
            if (to[x][p] != -1) {
                x = to[x][p];
            }
            cout << t[x];
        }
        cout << '\n';
    }

    return 0;
}