#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb emplace_back
#define AI(i) begin(i), end(i)
template<class T>
bool chmax(T &a, T b) { return a < b ? (a = b, true) : false; }
template<class T>
bool chmin(T &a, T b) { return b < a ? (a = b, true) : false; }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U>
void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
template<class T>
void debug(T L, T R) { while (L != R) cerr << *L << " \n"[next(L) == R], ++L; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
const int MAX_N = 3005, MAX_M = MAX_N * MAX_N / 3 << 1;
char w[MAX_N][MAX_N];
int n, m, a, b, id[MAX_N][MAX_N];
bool valid (char a, char b, char c) { return a == 'R' && b == 'G' && c == 'W'; }
array<int,3> edge[MAX_M];
int ma[MAX_M], vist[MAX_M], deg[MAX_M], lst[MAX_M];
int Time;
void expand(int x, int y) {
while (true) {
int u = ma[x];
ma[x] = y, ma[y] = x;
if (u == -1) return;
y = u, x = lst[y];
}
}
bool dfs(int x) {
queue<int> q;
q.push(x);
vist[x] = Time;
lst[x] = 0;
while (q.size()) {
int x = q.front(); q.pop();
for (int i = 0;i < deg[x];++i) {
int u = edge[x][i];
if (ma[u] == -1)
return expand(x, u), true;
lst[u] = x;
if (exchange(vist[u], Time) != Time)
q.emplace(ma[u]);
}
}
return false;
}
int max_clique() {
b += a;
memset(ma, -1, sizeof(ma));
int res = b;
for (int i = 1;i <= a;++i)
if (ma[i] == -1 && (Time = i, dfs(i)))
--res;
return res;
}
int solve() {
for (int i = 1;i <= n;++i)
for (int j = 1;j <= m;++j) {
if (valid(w[i][j-1], w[i][j], w[i][j+1]))
id[i][j] = ++a;
}
for (int i = 1;i <= n;++i)
for (int j = 1;j <= m;++j) {
if (valid(w[i-1][j], w[i][j], w[i+1][j])) {
++b;
for (int x : {id[i-1][j+1], id[i][j], id[i+1][j-1]}) if (x) {
edge[x][ deg[x]++ ] = b + a;
}
}
}
return max_clique();
}
int32_t main() {
ios_base::sync_with_stdio(0), cin.tie(0);
cin >> n >> m;
for (int i = 1;i <= n;++i)
cin >> w[i] + 1;
cout << solve() << '\n';
}
