#include <bits/stdc++.h>
using namespace std;
struct BIPARTITE_MATCHING {
const int undef = -1;
int n, m, matchingSize;
vector<bool> vis;
vector<int> pairL, pairR;
vector<vector<int>> adjL;
void init( int _n, int _m ) {
n = _n;
m = _m;
pairL.resize( n );
for ( int u = 0; u < n; u++ )
pairL[u] = undef;
pairR.resize( m );
for ( int v = 0; v < m; v++ )
pairR[v] = undef;
adjL.resize( n );
vis.resize( n );
}
void add_edge( int u, int v ) {
adjL[u].push_back( v );
}
bool findPair( int u ) {
if ( vis[u] )
return false;
vis[u] = true;
for ( int v: adjL[u] ) {
if ( pairR[v] == undef || findPair( pairR[v] ) ) {
pairL[u] = v;
pairR[v] = u;
return true;
}
}
return false;
}
void computeMaxMatching() {
bool newMatch = true;
while ( newMatch ) {
newMatch = false;
for ( int u = 0; u < n; u++ )
vis[u] = false;
for ( int i = 0; i < n; i++ ) {
int u = i;
if ( pairL[u] == undef && findPair( u ) )
newMatch = true;
}
}
matchingSize = 0;
for ( int u = 0; u < n; u++ ) {
if ( pairL[u] != undef )
matchingSize++;
}
}
} cuplaj;
const int MAX_N = 3000;
char mat[MAX_N][MAX_N];
int vertices[MAX_N][MAX_N][2];
int main() {
int n, m;
cin >> n >> m;
for ( int l = 0; l < n; l++ ) {
for ( int c = 0; c < m; c++ )
cin >> mat[l][c];
}
int nrVerticesSide0 = 0;
for ( int l = 0; l < n; l++ ) {
for ( int c = 0; c < m - 2; c++ ) {
if ( mat[l][c] == 'R' && mat[l][c + 1] == 'G' && mat[l][c + 2] == 'W' ) {
nrVerticesSide0++;
vertices[l][c][0] = nrVerticesSide0;
vertices[l][c + 1][0] = nrVerticesSide0;
vertices[l][c + 2][0] = nrVerticesSide0;
}
}
}
int nrVerticesSide1 = 0;
for ( int l = 0; l < n - 2; l++ ) {
for ( int c = 0; c < m; c++ ) {
if ( mat[l][c] == 'R' && mat[l + 1][c] == 'G' && mat[l + 2][c] == 'W' ) {
nrVerticesSide1++;
vertices[l][c][1] = nrVerticesSide1;
vertices[l + 1][c][1] = nrVerticesSide1;
vertices[l + 2][c][1] = nrVerticesSide1;
}
}
}
cuplaj.init( nrVerticesSide0 + 1, nrVerticesSide1 + 1 );
for ( int l = 0; l < n; l++ ) {
for ( int c = 0; c < m; c++ ) {
if ( vertices[l][c][0] != 0 && vertices[l][c][1] != 0 )
cuplaj.add_edge( vertices[l][c][0], vertices[l][c][1] );
}
}
cuplaj.computeMaxMatching();
cout << nrVerticesSide0 + nrVerticesSide1 - cuplaj.matchingSize << "\n";
}
