//#pragma GCC optimize("Ofast")
//#pragma GCC target("avx,avx2,sse,sse2,sse3,ssse3,sse4,abm,popcnt,mmx")
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef double db;
typedef long double ldb;
typedef complex<double> cd;

constexpr ll INF64 = 9'000'000'000'000'000'000, INF32 = 2'000'000'000, MOD = 1'000'000'007;
constexpr db PI = acos(-1);
constexpr bool IS_FILE = false, IS_TEST_CASES = false;

random_device rd;
mt19937 rnd32(rd());
mt19937_64 rnd64(rd());

template<typename T>
bool assign_max(T& a, T b) {
	if (b > a) {
		a = b;
		return true;
	}
	return false;
}

template<typename T>
bool assign_min(T& a, T b) {
	if (b < a) {
		a = b;
		return true;
	}
	return false;
}

template<typename T>
T square(T a) {
	return a * a;
}

template<>
struct std::hash<pair<ll, ll>> {
	ll operator() (pair<ll, ll> p) const {
		return ((__int128)p.first * MOD + p.second) % INF64;
	}
};

void solve() {
	ll n, m;
	cin >> n >> m;
	ll c, q;
	cin >> c >> q;
	vector<vector<char>> arr(n, vector<char>(m));
	vector<vector<char>> a1 = arr, a2 = arr;
	ll cb0 = 0, cb1 = 0;
	for (ll i = 0; i < n; i++) {
		for (ll j = 0; j < m; j++) {
			cin >> arr[i][j];
			if ((i + j) % 2 == 0) {
				a1[i][j] = 'G';
				a2[i][j] = 'R';
			} else {
				a1[i][j] = 'R';
				a2[i][j] = 'G';
			}
			if (arr[i][j] == 'B') {
				if ((i + j) % 2 == 0) {
					cb0++;
				} else {
					cb1++;
				}
			}
		}
	}
	ll c1 = 0, c2 = 0;
	for (ll i = 0; i < n; i++) {
		for (ll j = 0; j < m; j++) {
			if (arr[i][j] != 'B') {
				if (a1[i][j] != arr[i][j]) {
					c1++;
				}
				if (a2[i][j] != arr[i][j]) {
					c2++;
				}
			}
		}
	}
	if (c2 < c1) {
		swap(a1, a2);
	}
	ll nost = 0;
	if (cb1 < cb0) {
		nost = 1;
	}
	for (ll i = 0; i < n; i++) {
		for (ll j = 0; j < m; j++) {
			if (arr[i][j] != 'B' || (i + j) % 2 == nost) {
				arr[i][j] = a1[i][j];
			}
		}
	}
	for (auto i : arr) {
		for (auto j : i) {
			cout << j;
		}
		cout << '\n';
	}
}

int main() {
	if (IS_FILE) {
		freopen("", "r", stdin);
		freopen("", "w", stdout);
	}
    	ios_base::sync_with_stdio(false);
    	cin.tie(0);
    	cout.tie(0);
	ll t = 1;
	if (IS_TEST_CASES) {
		cin >> t;
	}
	for (ll i = 0; i < t; i++) {
		solve();
	}
}