#include <bits/stdc++.h>

std::vector<std::string> try_fuck(int n, int m, int q, std::vector<std::string> input) {
    int cnt = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            char a0 = input[i][j];
            std::string s = "RGB";
            if (i > 0) {
                std::erase(s, input[i - 1][j]);
            }
            if (j > 0) {
                std::erase(s, input[i][j - 1]);
            }
            if (!std::count(s.begin(), s.end(), input[i][j])) {
                std::string s2 = s;
                if (i + 1 < n) {
                    std::erase(s2, input[i + 1][j]);
                }
                if (j + 1 < m) {
                    std::erase(s2, input[i][j + 1]);
                }
                input[i][j] = s2.size() ? s2.front() : s.front();
            }
            cnt += input[i][j] != a0;
            // std::cout << input[i][j];
        }
        // std::cout << "\n";
    }
    if (cnt <= q) {
        return input;
    }
    return {};
}

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) {
        auto a = try_fuck(n, m, q, input);
        if (a.empty()) {
            std::vector<std::string> input2(m, std::string(n, '-'));
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    input2[j][i] = input[i][j];
                }
            }
            auto a2 = try_fuck(m, n, q, input2);
            if (a2.size()) {
                a = input;
                for (int i = 0; i < n; i++) {
                    for (int j = 0; j < m; j++) {
                        a[i][j] = a2[j][i];
                    }
                }
            }
        }
        for (auto s : a) {
            std::cout << s << "\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;
}