#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

const int N = 10, M = 1 << 10;

int n, m;
int g[1010];
int f[2][M][M];
vector<int> state;
int cnt[M];

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

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

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

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

    for (int i = 1; i <= n; i++)
        for (int j = 0; j < state.size(); j++)
            for (int k = 0; k < state.size(); k++)
                for (int u = 0; u < state.size(); u++) {
                    int a = state[j], b = state[k], c = state[u];
                    if (a & b | a & c | b & c) continue;
                    if (g[i] & b | g[i - 1] & a) continue;
                    f[i & 1][j][k] = max(f[i & 1][j][k], f[i - 1 & 1][u][j] + cnt[b]);
                }

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

    cout << res << endl;

    return 0;
}