#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define maxr 110
#define maxc 15
#define maxm 70
#define CL(a) memset(a,0,sizeof(a))
bool legal(int a, int b){ return a&b; }
int row, col;
int nums;
int base[maxr];
int state[maxm], soldier[maxm];
int dp[maxr][maxm][maxm];//第i行为j状态，i-1行为k状态，最大炮兵个数dp[i][j][k]
int main()
{
	//freopen("in.txt", "r", stdin);
	CL(base); CL(state); CL(soldier); CL(dp);
	nums = 0;
	char str[2][maxc];
	scanf("%d %d", &row, &col);
	for (int i = 0; i < row; i++)  //将地图转换成二进制
	{
		scanf("%s", str[0]);
		for (int j = 0; j < col;j++)
		if (str[0][j] == 'H') base[i] += 1 << j;
	}
 
	for (int i = 0; i < (1<<col); i++){  //确立仅仅是两个炮兵互不攻击的状态
		if (legal(i, i << 2) || legal(i, i << 1)) continue; //dont forget case: d=1
		int k = i;
		while (k){
			soldier[nums] += k & 1;
			k = k >> 1;
		}
		state[nums++] = i;
	}
 
	for (int i = 0; i < nums; i++)  //初始化
	{
		if (legal(state[i], base[0])) continue; //去除炮兵在山上的
		dp[0][i][0] = soldier[i];
	}
 
	for (int r = 1; r < row; r++)  //每一行
	{
		for (int i = 0; i < nums; i++)  //第i行状态
		{
			if (legal(state[i], base[r])) continue; //去除炮兵在山上的
			for (int j = 0; j < nums; j++) //第i-1行状态
			{
				if (legal(state[j], base[r-1])) continue; //去除炮兵在山上的
				if (legal(state[i], state[j])) continue;  //除去上下两行相互攻击
				for (int k = 0; k < nums; k++) //第i-2行状态
				{
					if (r - 2 >= 0 && legal(state[k], base[r - 2])) continue; //去除炮兵在山上的
					if (legal(state[i], state[k])) continue;  //除去上下两行相互攻击
					if (legal(state[j], state[k])) continue;  //除去上隔一行下两行相互攻击
					dp[r][i][j] = max(dp[r][i][j], dp[r - 1][j][k] + soldier[i]);
				}
			}
		}
	}
	int ans = 0;
	for (int i = 0; i < nums; i++)
	for (int j = 0; j < nums; j++)
		ans = max(ans, dp[row - 1][i][j]);
	printf("%d\n", ans);
	return 0;
}