#include <bits/stdc++.h>
using namespace std;
#define INF 16000001
typedef pair<int, int> pii;
int main() {
int h, w;
cin >> h >> w;
char grid[h + 2][w + 2];
for (int i = 0; i <= h + 1; i++) {
for (int j = 0; j <= w + 1; j++) {
if (i < 1 || i > h || j < 1 || j > w) grid[i][j] = '.';
else cin >> grid[i][j];
}
}
int d[h + 1][w + 1];
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
d[i][j] = INF;
}
}
d[h][w] = 0;
deque<pii> q;
q.push_front({h, w});
bool processed[h + 1][w + 1] = {};
while (!q.empty()) {
int a, b;
tie(a, b) = q.front();
q.pop_front();
if (processed[a][b]) continue;
processed[a][b] = true;
if (grid[a + 1][b] != '.' && d[a + 1][b] > d[a][b] + (grid[a + 1][b] != grid[a][b])) {
d[a + 1][b] = d[a][b] + (grid[a + 1][b] != grid[a][b]);
if (grid[a + 1][b] != grid[a][b]) q.push_back({a + 1, b});
else q.push_front({a + 1, b});
}
if (grid[a - 1][b] != '.' && d[a - 1][b] > d[a][b] + (grid[a - 1][b] != grid[a][b])) {
d[a - 1][b] = d[a][b] + (grid[a - 1][b] != grid[a][b]);
if (grid[a - 1][b] != grid[a][b]) q.push_back({a - 1, b});
else q.push_front({a - 1, b});
}
if (grid[a][b + 1] != '.' && d[a][b + 1] > d[a][b] + (grid[a][b + 1] != grid[a][b])) {
d[a][b + 1] = d[a][b] + (grid[a][b + 1] != grid[a][b]);
if (grid[a][b + 1] != grid[a][b]) q.push_back({a, b + 1});
else q.push_front({a, b + 1});
}
if (grid[a][b - 1] != '.' && d[a][b - 1] > d[a][b] + (grid[a][b - 1] != grid[a][b])) {
d[a][b - 1] = d[a][b] + (grid[a][b - 1] != grid[a][b]);
if (grid[a][b - 1] != grid[a][b]) q.push_back({a, b - 1});
else q.push_front({a, b - 1});
}
}
int ans = 0;
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
if (grid[i][j] != '.') ans = max(ans, d[i][j]);
}
}
cout << ans + 1 << endl;
return 0;
}
