#include <bits/stdc++.h>
using namespace std;
vector<string> matrix;
vector<vector<int>> dir{{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
int inside(int x, int y, int h, int w) {
return x >= 0 and x < h and y >= 0 and y < w and matrix[x][y] != '.';
}
int main() {
int h, w;
cin >> h >> w;
matrix.resize(h);
for(int i = 0; i < h; i++) {
cin >> matrix[i];
}
deque<pair<int, int>> q;
vector<vector<int>> cost(h, vector<int>(w, INT_MAX));
q.push_front({0, 0});
cost[0][0] = 1;
int maxVal = 1;
while(!q.empty()) {
int x = q.front().first;
int y = q.front().second;
q.pop_front();
for(int i = 0; i < 4; i++) {
int nx = x + dir[i][0];
int ny = y + dir[i][1];
if(inside(nx, ny, h, w) and cost[nx][ny] == INT_MAX) {
if(matrix[nx][ny] == matrix[x][y]) {
q.push_front({nx, ny});
cost[nx][ny] = cost[x][y];
}
else {
q.push_back({nx, ny});
cost[nx][ny] = cost[x][y] + 1;
}
maxVal = max(maxVal, cost[nx][ny]);
}
}
}
cout << maxVal << endl;
}
