#include<bits/stdc++.h>
using namespace std;
const int maxn = 117, maxm = 11;
int n, m, ans, state[maxn], f[2][1 << maxm][1 << maxm]; //last now
inline int calc(int x) {
	int cnt = 0;
	while (x)++cnt, x &= x - 1;
	return cnt;
}
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	cin >> n >> m;
	for (int i = 1; i <= n; ++i) {
		int buff = 1 << (m - 1);
		for (int j = 1; j <= m; ++j) {
			char c;
			cin >> c;
			state[i] += (c == 'H') * buff;
			buff >>= 1;
		}
	}
	for (int i = 0; i < (1 << m); ++i) {
		if ((i & state[1]) || (i & (i >> 1)) || (i & (i >> 2)) || (i & (i << 1)) || (i & (i << 2)))
			continue;
		f[1 & 1][0][i] = calc(i);
		for (int j = 0; j < (1 << m); ++j) {
			if ((i & j) || (j & state[2]) || (j & (j >> 1)) || (j & (j >> 2)) || (j & (j << 1)) || (j & (j << 2)))
				continue;
			f[2 & 1][i][j] = f[1 & 1][0][i] + calc(j);
		}
	}
	for (int l = 3; l <= n; ++l) {
		for (int i = 0; i < (1 << m); ++i) {
			if ((i & state[l - 2]) || (i & (i >> 1)) || (i & (i >> 2)) || (i & (i << 1)) || (i & (i << 2)))
				continue;
			for (int j = 0; j < (1 << m); ++j) {
				if ((i & j) || (j & state[l - 1]) || (j & (j >> 1)) || (j & (j >> 2)) || (j & (j << 1)) || (j & (j << 2)))
					continue;
				for (int k = 0; k < (1 << m); ++k) {
					if ((i & k) || (j & k) || (k & state[l]) || (k & (k >> 1)) || (k & (k >> 2)) || (k & (k << 1)) || (k & (k << 2)))
						continue;
					f[l & 1][j][k] = f[l - 1 & 1][i][j] + calc(k);
				}
			}
		}
	}
	for (int i = 0; i < (1 << m); ++i)
		for (int j = 0; j < (1 << m); ++j)
			ans = max(ans, f[n & 1][i][j]);
	cout << ans << '\n';
	return 0;
}

$RECORD$