#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
#define endl '\n'
#define ll long long
#define pi pair<int, int>
#define f first
#define s second
const int mxn = 3002, k = 2, w = 3;
const char c[w] = {'R', 'G', 'W'};
const int dx[k << 1] = {-1, 0, 1, 0};
const int dy[k << 1] = {0, -1, 0, 1};
int n, m;
int a[mxn][mxn], b[mxn][mxn];
int dp[mxn][mxn][2];
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
for(int i = 1; i <= n; i++)
for(int j = 1; j <= m; j++){
char x;
cin >> x;
a[i][j] = find(c, c + w, x) - c;
}
int ret = 0;
for(int i = 1; i <= n; i++)
for(int j = 1; j <= m; j++){
if(!~-a[i][j]){
for(int p = 0; p < k; p++){
b[i][j] ^= 1 << p;
for(int l = 0; l < 2; l++){
int x = i + dx[(p + l * k) % (2 * k)], y = j + dy[(p + l * k) % (2 * k)];
if(x < 1 || y < 1 || x > n || y > m || a[x][y] != 2 * l){
b[i][j] ^= 1 << p;
break;
}
}
}
}
for(int p = 0; p < 2; p++)
for(int l = 0; l < 2; l++){
int x = ((b[i][j] >> p) & 1), y = ((b[i - 1][j + 1] >> l) & 1);
if(p == l || !x || !y){
dp[i][j][p] = max(dp[i][j][p], dp[i - 1][j + 1][l] + x);
}
}
if(i == n || !~-j) ret += max(dp[i][j][0], dp[i][j][1]);
}
cout << ret << endl;
return 0;
}
