#include <bits/stdc++.h>

using namespace std;

const int M = 12, N = 110;

int f[2][1 << M][1 << M];
int n, m;
int g[N], cnt[1 << M];
vector<int> legal;

int count(int x)
{
    int res = 0;
    for (int i = 0; i < m; i ++ ) res += (x >> i & 1);
    return res;
}

bool check(int x)
{
    for (int i = 0; i < m; i ++ )
        if ((x >> i & 1) && ((x >> i + 1 & 1) || (x >> i + 2 & 1))) return false;
    return true;
}

int main()
{
    scanf("%d%d", &n, &m);

    for (int i = 1; i <= n; i ++ )
    {
        string s;
        cin >> s;
        for (int j = 0; j < m; j ++ ) g[i] += (s[j] == 'H') << j;
    }

    for (int i = 0; i < 1 << m; i ++ ) if (check(i)) legal.push_back(i), cnt[i] = count(i);

    for (int i = 1; i <= n; i ++ )
        for (int j = 0; j < legal.size(); j ++ )
            if ((g[i] & legal[j]) == 0)
                for (int k = 0; k < legal.size(); k ++ )
                    if ((g[i - 1] & legal[k]) == 0)
                        for (int l = 0; l < legal.size(); l ++ )
                            if (!(legal[j] & legal[k]) && !(legal[j] & legal[l]) && !(legal[l] & legal[k]))
                                f[i & 1][k][j] = max(f[i & 1][k][j], f[i - 1 & 1][l][k] + cnt[legal[j]]);

    int res = 0;
    for (int i = 0; i < legal.size(); i ++ )
        for (int j = 0; j < legal.size(); j ++ )
            res = max(res, f[n & 1][i][j]);

    printf("%d\n", res);

    return 0;
}