#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ld double
#define sz(x) (int)x.size()
#define all(x) x.begin(),x.end()
#define pb emplace_back
#define X first
#define Y second
const int N = 3005;
typedef pair<int,int> ii;
char a[N][N];
int t[N][N];
struct Edge {
int v, c;
Edge(int _v,int _c) : v(_v), c(_c) {}
};
vector<Edge> E;
vector<int> g[N * N];
void addEdge(int u,int v,int c) {
g[u].pb(sz(E)); E.pb(v,c);
g[v].pb(sz(E)); E.pb(u,0);
}
int S, T;
int d[N * N];
int p[N * N];
bool bfs() {
for(int i = 0 ; i <= T ; ++i)
d[i] = -1,
p[i] = 0;
queue<int> q;
q.push(S); d[S] = 0;
while (q.size()) {
int u = q.front(); q.pop();
for(int i : g[u]) {
int v = E[i].v;
if (E[i].c == 0) continue;
if (d[v] < 0) {
d[v] = d[u] + 1;
q.push(v);
}
}
}
return d[T] >= 0;
}
int dfs(int u,int F) {
if (u == T || F == 0) return F;
for(int &i = p[u] ; i < sz(g[u]) ; ++i) {
int j = g[u][i];
int v = E[j].v;
if (E[j].c == 0 || d[v] != d[u] + 1)
continue;
int res = dfs(v,min(E[j].c,F));
if (res) {
E[j].c -= res; j ^= 1;
E[j].c += res; return res;
}
}
return 0;
}
int MaxFlow() {
while (bfs())
while (dfs(S,1));
int ans = 0;
for(int i : g[T])
ans += E[i].c;
return ans;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int n; cin >> n;
int m; cin >> m;
int cnt = 0;
for(int i = 0 ; i < n ; ++i)
for(int j = 0 ; j < m ; ++j) {
cin >> a[i][j];
if (a[i][j] != 'G')
t[i][j] = cnt++;
if (a[i][j] == 'W') {
if (i > 1 && a[i - 1][j] == 'G' && a[i - 2][j] == 'R')
addEdge(t[i][j],t[i - 2][j],1);
if (j > 1 && a[i][j - 1] == 'G' && a[i][j - 2] == 'R')
addEdge(t[i][j],t[i][j - 2],1);
}
}
S = cnt;
T = cnt + 1;
for(int i = 0 ; i < n ; ++i)
for(int j = 0 ; j < m ; ++j) {
if (a[i][j] == 'W') addEdge(S,t[i][j],1);
if (a[i][j] == 'R') addEdge(t[i][j],T,1);
}
cout << MaxFlow() << endl;
}
