#include<bits/stdc++.h>
using namespace std;
#define ss second
#define ff first
typedef pair<int, int> pii;
const int lim = 4e3+5;
char c[lim][lim];
int d[lim][lim];
bool marc[lim][lim];
int H, W, ans;
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
bool inbound(int x, int y){
return 1<=x&&x<=H && 1<=y&&y<=W;
}
int main(){
cin.tie(0)->sync_with_stdio(0);
cin >> H >> W;
for(int i = 1; i <= H; i++){
for(int j = 1; j <= W; j++){
cin >> c[i][j];
}
}
deque<pii> dq;
dq.push_back({1, 1});
d[1][1] = 1;
marc[1][1] = true;
while(!dq.empty()){
auto [x, y] = dq.front();
dq.pop_front();
ans = max(ans, d[x][y]);
for(int i = 0; i < 4; i++){
int nx = x+dx[i], ny = y+dy[i];
if(c[nx][ny] == '.' || !inbound(nx, ny) || marc[nx][ny]) continue;
if(c[nx][ny] == c[x][y]){
d[nx][ny] = d[x][y];
dq.push_front({nx, ny});
marc[nx][ny] = true;
}
else{
d[nx][ny] = d[x][y]+1;
dq.push_back({nx, ny});
marc[nx][ny] = true;
}
}
}
cout << ans << '\n';
}
