#include <bits/stdc++.h>

int32_t main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int n, m, c, q;
    std::cin >> n >> m >> c >> q;
    std::vector<std::string> input(n);
    for (auto& i : input) {
        std::cin >> i;
    }

    auto select = [&](int s, int i, int j) -> char {
        return "RGGBRB"[s / 2 * 2 + (s + i + j & 1)];
    };
    int suc = -1;
    for (int s = 0; s < 6; s++) {
        int cnt = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                cnt += input[i][j] != select(s, i, j);
            }
        }
        if (cnt <= q) {
            suc = s;
            break;
        }
    }

    if (suc == -1) {
        std::vector<int> fuck;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                fuck.clear();
                if (i > 0) {
                    fuck.push_back(input[i - 1][j]);
                }
                if (j > 0) {
                    fuck.push_back(input[i][j - 1]);
                }
                std::string s = "RGB";
                for (char ch : fuck) {
                    std::erase(s, ch);
                }
                if (!std::count(s.begin(), s.end(), input[i][j])) {
                    std::string s2 = s;
                    if (j + 1 < n) {
                        std::erase(s2, input[i][j + 1]);
                    }
                    input[i][j] = s2.size() ? s2.front() : s.front();
                }
                std::cout << input[i][j];
            }
            std::cout << "\n";
        }
        return 0;
    }

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            std::cout << select(suc, i, j);
        }
        std::cout << std::endl;
    }

    return 0;
}