#include<bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define int long long
//#define int double
typedef pair<int,int> pii;
typedef vector<pii> vii;
typedef vector<int> vi;
typedef vector<bool> vb;
#define FOR(i,a) for(int i=0;i<(a);i++)
#define FORE(i,a,b) for(int i=(a);i<(b);i++)
#define all(x) x.begin(),x.end()
#define fi first
#define se second
#define pb push_back
#define sp <<" "<<
#define cont(x) for(auto el:x) cout<<el<<' ';cout<<endl;
#define contp(x) for(auto el:x) cout<<el.fi<<'-'<<el.se<<' ';cout<<endl;
#define DEBUG(x) cout<<#x sp x<<endl;
#define carp(x,y) ((x%MOD)*(y%MOD))%MOD
#define topla(x,y) ((x%MOD)+(y%MOD))%MOD
#define mid (l+r)/2
const int MAXN=3e3+5;
const int MOD=1e9+7;
const int INF=1e18;
int say[MAXN][MAXN];
int ans;
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
ans=0;
int n,m;
cin>>n>>m;
vector<string> grid(n);
vector<vb> used(n, vb(m,false));
FOR(i,n){
cin>>grid[i];
FOR(j,m){
if(grid[i][j]=='W'){
if(j-2>=0){
if(grid[i][j-1]=='G' and grid[i][j-2]=='R'){
used[i][j-2]=used[i][j-1]=used[i][j]=true;
}
}
if(i-2>=0){
if(grid[i-1][j]=='G' and grid[i-2][j]=='R'){
used[i-2][j]=used[i-1][j]=used[i][j]=true;
}
}
}
}
}
int bir,iki,uc;
bir=iki=uc=0;
FOR(i,n){
FOR(j,m){
if(used[i][j]){
if(grid[i][j]=='R') bir++;
else if(grid[i][j]=='G') iki++;
else uc++;
}
}
}
cout<<min({bir,iki,uc})<<endl;
}
