#include<bits/stdc++.h>
using namespace std;
int n,m,mapi[110],con[1<<11],js[1<<11],f[1<<11][1<<11][110],cnt;
int lowbiti(int x){
	int tot=0;
	while(x){
		if(x&1)++tot;
		x=x>>1;
	}
	return tot;
}
int main(){
	char ch;
	scanf("%d %d",&n,&m);
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			cin>>ch;
			mapi[i]=(mapi[i]<<1)+(ch=='H'?1:0);
		}
	}
	for(int i=0;i<(1<<m);i++){
		if((i&(i<<1))==0&&(i&(i<<2))==0&&(i&(i>>1))==0&&(i&(i>>2))==0){
			++cnt;
			con[cnt]=i;
			js[cnt]=lowbiti(i);
		}
	}
	for(int i=1;i<=cnt;i++){
		if((mapi[1]&con[i])==0){
			f[0][i][1]=js[i];
		}
	}
	for(int i=1;i<=cnt;i++){
		if((mapi[2]&con[i])==0){
			for(int j=1;j<=cnt;j++){
				if((mapi[1]&mapi[j])==0&&(con[i]&con[j])==0)
					f[j][i][2]=js[i]+js[j];
			}
		}
	}
	for(int i=3;i<=n;i++){//i
		for(int j=1;j<=cnt;j++){//the condition of i line
			if((mapi[i]&con[j])==0){
				for(int k=1;k<=cnt;k++){//the condition of i-1 line
					if((mapi[i-1]&con[k])==0&&(con[j]&con[k])==0){
						for(int l=1;l<=cnt;l++){//the condition of l-2 line
							if((mapi[i-2]&con[l])==0&&(con[l]&con[k])==0&&(con[j]&con[l])==0)
								f[k][j][i]=max(f[k][j][i],f[l][k][i-1]+js[j]);
						}
					}
				}
			}
		}
	}
	int ans=0;
	for(int i=1;i<=cnt;i++){
		for(int j=1;j<=cnt;j++){
			ans=max(ans,f[i][j][n]);
		}
	}
	cout<<ans;
	return 0;
}