#include<algorithm>
#include<iostream>
#include<vector>
using namespace std;

int n, m;
bool G[50][20];

int main() {
	cin >> n >> m;
	for (int i=n-1; i >= 0; i--) {
		string line;
		cin >> line;
		for (int j=0; j < m; j++)
			G[i/2][j] |= line[j] == '#';
	}

	vector<int> lastcans;
	int result = 0;
	for (int row = n/2 - 1; row >= 0; row--) {
		vector<int> curcans1, curcans2;

		// delay placing cans, and if needed place to the right:
		for (int col = 0; col < m; col++) {
			// do we need to place a can here?
			if (G[row][col] || (find(lastcans.begin(), lastcans.end(), col-1) != lastcans.end() && (curcans1.empty() || curcans1.back() != col-2))) {
				curcans1.push_back(col);
				if (++col == m) {
					// move others
					for (int it = curcans1.size(), pos = m-1; it-- && curcans1[it] == pos; pos -= 2)
						curcans1[it]--;
				}
			}
		}

		// delay placing cans, and if needed place to the left:
		for (int col = m-1; col >= 0; col--) {
			// do we need to place a can here?
			if (G[row][col] || (find(lastcans.begin(), lastcans.end(), col) != lastcans.end() && (curcans2.empty() || curcans2.back() != col+1))) {
				curcans2.push_back(col-1);
				if (--col < 0) {
					// move others
					for (int it = curcans2.size(), pos = -1; it-- && curcans2[it] == pos; pos += 2)
						curcans2[it]++;
				}
			}
		}

		// now take the best option of the two:
		lastcans = curcans1.size() < curcans2.size() ? curcans1 : curcans2;
		result += lastcans.size();
	}
	cout << result << endl;
	return 0;
}