#include<algorithm>
#include<iostream>
#include<iomanip>
#include<cstring>
#include<cstdio>
#include<cmath>
#define lowbit(x) (x&-x)
#define LL long long
using namespace std;
int read()
{
	int s=0,bj=0;
	char ch=getchar();
	while(ch<'0'||ch>'9')bj|=(ch=='-'),ch=getchar();
	while(ch>='0'&&ch<='9')s=(s<<1)+(s<<3)+(ch^48),ch=getchar();
	return bj?-s:s;
}
void printnum(int x)
{
	if(x>9)printnum(x/10);
	putchar(x%10^48);
}
void print(int x,char ch)
{
	if(x<0){putchar('-');x=-x;}
	printnum(x);putchar(ch);
}
int n,m,f[1<<10][1<<10][3];//no lst
int a[15],sum[71],bj[71],cnt,ans;char ch[15];
int Sum(int x)
{
	int num=0;
	while(x){x-=lowbit(x);++num;}
	return num;
}
int main()
{
	n=read();m=read();
	for(int i=1;i<=n;++i)
	{
		scanf("%s",ch);
		for(int j=0;j<m;++j)
		{
			a[i]<<=1;
			a[i]+=ch[j]=='H';
		}
	}
	for(int i=0;i<(1<<m);++i)if(!(i&(i<<1)||(i&(i<<2)))){sum[++cnt]=Sum(i);bj[cnt]=i;}
//	for(int i=1;i<=cnt;++i)if(!(bj[i]&a[1]))f[i][0][1]=sum[i];
	for(int i=1;i<=cnt;++i)
	for(int j=1;j<=cnt;++j)
	{
		if(bj[i]&bj[j]||bj[i]&a[2]||bj[j]&a[1])continue;
		f[i][j][2]=sum[i]+sum[j];//i,j,2
	}
	for(int i=3;i<=n;++i)
	for(int j=1;j<=cnt;++j)//no
	{
		if(bj[j]&a[i])continue;
		for(int k=1;k<=cnt;++k)
		{
			if((bj[k]&a[i-1])||(bj[j]&bj[k]))continue;//lst
			for(int l=1;l<=cnt;++l)//lst2
			{
				if((bj[l]&bj[k])||(bj[l]&bj[j])||(bj[l]&a[i-2]))continue;
				f[j][k][i%3]=max(f[j][k][i%3],f[k][l][(i-1)%3]+sum[j]);
			}
		}
	}
	for(int i=1;i<=cnt;++i)
	for(int j=1;j<=cnt;++j)ans=max(ans,f[i][j][n%3]);
	print(ans,'\n');
	return 0;
}