#include <iostream>
using namespace std;
 
int main() {
	int w, h, res = 0;
	cin >> w >> h;
	char **x = new char *[h];
	for (int i = 0; i < h; i++) x[i] = new char[w];
	for (int i = 0; i < h; i++) {
		for (int j = 0; j < w; j++) {
			cin >> x[i][j];
		}
	}
	for (int i = 0; i < h; i++) {
		for (int j = 0; j < w - 1; j++) {
			if (x[i][j] != x[i][j + 1]) res++;
		}
	}
	for (int i = 0; i < h - 1; i++) {
		for (int j = 0; j < w; j++) {
			if (x[i][j] != x[i + 1][j]) res++;
		}
	}
	cout << res << endl;
	return 0;
}

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