#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define sz(x) int(x.size())
#define fast ios_base :: sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
#define loop(i, j, n, k) for(int i = j; i <= n; i += k)
#define reloop(i, j, n, k) for (int i = j; i >= n; i +=k)
using ll = long long;
using vi = vector<int>;
using vll = vector<long long>;
using pii = pair<int,int>;
using pss = pair<string,string>;
const int N = 4e3;
char a[N + 5][N + 5];
int dx[4] = {0, 0, -1, 1};
int dy[4] = {1, -1, 0, 0};
int n, m, depth[N + 5][N + 5];
int ans = 1;
deque<pii>q;
bool inside (int x, int y){
if (x < 1 || x > n || y < 1 || y > m || a[x][y] == '.')
return false;
return true;
}
int main(){
cin >> n >> m;
loop(r, 1, n, 1)
loop(c, 1, m, 1)
cin >> a[r][c];
q.push_front({1, 1});
depth[1][1] = 1;
while(!q.empty()){
pii top = q.front(); q.pop_front();
int x = top.fi, y = top.se;
ans = max(ans, depth[x][y]);
loop(k, 0, 3, 1){
int nx = x + dx[k], ny = y + dy[k];
if (inside(nx, ny) && depth[nx][ny] == 0){
if (a[nx][ny] == a[x][y]){
depth[nx][ny] = depth[x][y];
q.push_front({nx, ny});
}else{
depth[nx][ny] = depth[x][y] + 1;
q.push_back({nx, ny});
}
}
}
}
cout << ans;
}
