#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
#include <unordered_map>
#include <functional>
int gs_left, gs_right;
int x, y;
char arr[3005][3005];
std::vector<bool> real_node;
std::vector<char> color;
std::vector<std::vector<int>> adj_list;
int Not(int node) {
return ((node < x*y) ? node+x*y : node-x*y);
}
inline bool ok_line(int i, int j) {
return arr[i][j] == 'R' && arr[i][j+1] == 'G' && arr[i][j+2] == 'W';
}
inline bool ok_column(int i, int j) {
return arr[i][j] == 'R' && arr[i+1][j] == 'G' && arr[i+2][j] == 'W';
}
void dfs(int k, int c) {
color[k] = c;
for (const auto& i : adj_list[k]) {
if (color[i]==-1) {
dfs(i, c^1);
}
else {
if (color[i]==color[k]) {
exit(1);
}
}
}
}
void build_graph() {
for (int i = 0; i < x; i++) {
for (int j = 0; j+2 < y; j++) {
if (ok_line(i,j)) {
real_node[i*y+j] = 1;
if (i+2 < x && ok_column(i,j)) {
adj_list[i*y+j].emplace_back(Not(i*y+j));
}
if (i-1 >= 0 && i+1 < x && ok_column(i-1,j+1)) {
adj_list[i*y+j].emplace_back(Not((i-1)*y+j+1));
}
if (i-2 >= 0 && ok_column(i-2,j+2)) {
adj_list[i*y+j].emplace_back(Not((i-2)*y+j+2));
}
}
}
}
for (int i = 0; i+2 < x; i++) {
for (int j = 0; j < y; j++) {
if (ok_column(i,j)) {
real_node[Not(i*y+j)] = 1;
if (j+2 < y && ok_line(i,j)) {
adj_list[Not(i*y+j)].emplace_back(i*y+j);
}
if (j-1 >= 0 && j+1 < y && ok_line(i+1,j-1)) {
adj_list[Not(i*y+j)].emplace_back((i+1)*y+j-1);
}
if (j-2 >= 0 && ok_line(i+2,j-2)) {
adj_list[Not(i*y+j)].emplace_back((i+2)*y+j-2);
}
}
}
}
for (int i = 0; i < 2*x*y; i++) {
if (real_node[i]&&color[i]==-1) {
dfs(i, 0);
}
}
}
void normalize_graph() {
std::unordered_map<int,int> norm_l;
for (int i = 0; i < 2*x*y; i++) {
if (real_node[i]&&color[i]==0) {
norm_l[i] = 0;
}
}
for (auto& i : norm_l) {
i.second = ++gs_left;
}
std::unordered_map<int,int> norm_r;
for (int i = 0; i < 2*x*y; i++) {
if (real_node[i]&&color[i]==1) {
norm_r[i] = 0;
}
}
for (auto& i : norm_r) {
i.second = ++gs_right;
}
//std::cout << gs_left << " " << gs_right << "\n";
std::vector<std::vector<int>> new_adj(std::max(gs_left, gs_right)+1);
for (int i = 0; i < 2*x*y; i++) {
if (real_node[i]&&color[i]==0) {
for (const auto& j : adj_list[i]) {
//std::cout << norm[i] << " " << norm[j] << "\n";
new_adj[norm_l[i]].emplace_back(norm_r[j]);
}
}
}
adj_list = new_adj;
}
void max_bipartite_matching() {
std::vector<int> match_left(6000005, -1);
std::vector<int> match_right(6000005, -1);
std::vector<char> vis(6000005, 0);
const std::function<bool(int)> dfs = [&](int k) {
if (vis[k]) {
return false;
}
vis[k] = 1;
for (const auto& i : adj_list[k]) {
if (match_right[i] == -1 || dfs(match_right[i])) {
match_left[k] = i;
match_right[i] = k;
return true;
}
}
return false;
};
while (1) {
std::fill(vis.begin(), vis.end(), 0);
bool done = 1;
for (int i = 1; i <= gs_left; i++) {
if (match_left[i] == -1) {
done &= !dfs(i);
}
}
if (done) {
break;
}
}
int ret = 0;
for (int i = 1; i <= gs_left; i++) {
ret += (match_left[i]!=-1);
}
//std::cout << ret << "\n";
std::cout << gs_left + gs_right - ret << "\n";
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(NULL);
std::cout.tie(NULL);
std::cin >> x >> y;
adj_list.resize(2*x*y);
real_node.assign(2*x*y,0);
color.assign(2*x*y,-1);
for (int i = 0; i < x; i++) {
std::cin >> arr[i];
}
build_graph();
normalize_graph();
max_bipartite_matching();
}
