#include<bits/stdc++.h>
using namespace std;
#define __ ios_base::sync_with_stdio(false); cin.tie(NULL);
typedef long long ll;
#define pb push_back
const vector<vector<int>> directions = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
vector<vector<int>> vis(4001,vector<int>(4001));
int main(){__
int H, W; cin >> H >> W;
int operations = 0;
int maxi = 0;
vector<string> grid(H);
for (int i = 0; i < H; i++) cin >> grid[i];
vector<vector<int>> distance(H, vector<int>(W, 1e9));
for(int i = 0; i < H; i++){
for(int j = 0; j < W; j++){
cin >> grid[i][j];
}
}
deque<vector<int>> d;
d.push_front({0, 0, 0});
distance[0][0] = 0;
while(!d.empty()){
vector<int> a = d.front();
int x = d.front()[0];
int y = d.front()[1];
int w = d.front()[2];
d.pop_front();
maxi = max(maxi, distance[x][y]);
if(vis[x][y]) continue;
vis[x][y]=1;
for(auto dir : directions){
int nx = x + dir[0];
int ny = y + dir[1];
if(nx < 0 || ny < 0 || nx >= H || ny >= W) continue;
if(grid[nx][ny] == '.') continue;
int nw = !(grid[x][y] == grid[nx][ny]);
if(distance[x][y] + nw < distance[nx][ny]){
//cout << nx << " " << ny << "\n";
distance[nx][ny] = distance[x][y] + nw;
if(nw == 1){
d.push_back({nx, ny, nw});
}
else if(nw == 0){
d.push_front({nx, ny, nw});
}
}
}
}
cout << maxi + 1;
}
