#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 3e3 + 3, M = 3e6 + 3;
int n, m, _n, _m, id[N][N], iter = 0;
basic_string <int> g[M];
char a[N][N];
bool col[N][N];
bool stick(char A, char B, char C) {
if (A == 'R' && B == 'G' && C == 'W') return true;
return false;
}
vector <int> seen, dist, matchL, matchR;
bool dfs(int u) {
if(seen[u] == iter) return 0;
seen[u] = iter;
for(int v : g[u]) {
if(matchR[v] == -1) {
matchL[u] = v;
matchR[v] = u;
return 1;
}
}
for(int v : g[u]) {
if(dist[matchR[v]] == dist[u] + 1 && dfs(matchR[v])) {
matchL[u] = v;
matchR[v] = u;
return 1;
}
}
return 0;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
// freopen(".INP", "r", stdin);
// freopen(".OUT", "w", stdout);
cin >> _n >> _m;
for (int i=1;i<=_n;++i)
for (int j=1;j<=_m;++j) cin >> a[i][j];
for (int i=1;i<=_n;++i) {
for (int j=1;j<=_m;++j) {
if (stick(a[i][j], a[i + 1][j], a[i + 2][j])) {
col[i][j] = 1;
id[i][j] = ++n;
}
if (stick(a[i][j], a[i][j + 1], a[i][j + 2])) {
m++;
if (col[i][j]) g[id[i][j]].push_back(m);
if (col[i - 1][j + 1]) g[id[i - 1][j + 1]].push_back(m);
if (i != 1 && col[i - 2][j + 2]) g[id[i - 2][j + 2]].push_back(m);
}
}
}
matchL.assign(n + 1, -1);
matchR.assign(m + 1, -1);
dist.assign(n + 1, 0);
seen.assign(n + 1, 0);
int ans = 0;
while (1) {
queue <int> q;
for(int u = 1; u <= n; ++u) {
if(matchL[u] == -1) dist[u] = 0, q.push(u);
else dist[u] = -1;
}
while(q.size()) {
int u = q.front();
q.pop();
for(int v : g[u]) {
if(matchR[v] != -1 && dist[matchR[v]] == -1) {
dist[matchR[v]] = dist[u] + 1;
q.push(matchR[v]);
}
}
}
int add = 0;
++iter;
for(int u = 1; u <= n; ++u)
if(matchL[u] == -1) add += dfs(u);
if(add == 0) break;
ans += add;
}
cout << n + m - ans;
}
