#include<bits/stdc++.h>
using namespace std;
int h , w;
vector<string>grid;
int dx[4] = {1, -1, 0 , 0};
int dy[4] = {0 , 0 , 1 , -1};
bool inside(int y , int x) {
return (x > -1 && y > -1 && x < w && y < h && grid[y][x] != '.');
}
int main() {
cin >> h >> w;
grid.resize(h);
for(int i = 0; i < h ;i++) {
cin >> grid[i];
}
deque<pair<int,int>> q;
q.push_back({0 , 0 });
vector<vector<int>>depth(h , vector<int>(w));
int ans = 1;
depth[0][0] = 1;
while(!q.empty()) {
int ycord = q.front().first;
int xcord = q.front().second;
q.pop_front();
ans = max(ans, depth[ycord][xcord]);
for(int i = 0;i < 4 ;i++) {
int x = xcord + dx[i];
int y = ycord + dy[i];
if(!inside(y , x) || depth[y][x] != 0) {
continue;
}
if(grid[ycord][xcord] == grid[y][x]) {
q.push_front({y, x});
depth[y][x] = depth[ycord][xcord];
}
else {
q.push_back({y, x});
depth[y][x] = depth[ycord][xcord] + 1;
}
}
}
cout << ans << endl;
}
