#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vc = vector<char>;
using vvc = vector<vc>;
const ll mod = 1e9 + 7,inf = 1e18;
const vi dx = {1,-1,0,0},dy = {0,0,1,-1};
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int main()
{
fast;
int w,h;
cin>>w>>h;
vvc g(w,vc(h));
for (int i = 0;i<w;i++)for (int j = 0;j<h;j++)cin>>g[i][j];
vvi dp(w,vi(h,1e9));
dp[0][0] = 0;
deque<pair<int,int>>q;
q.push_back({0,0});
int ans = 0;
while (!q.empty()){
int ci = q.front().first,cj = q.front().second;
q.pop_front();
for (int x = 0;x<4;x++){
int ni = ci + dx[x],nj = cj + dy[x];
if (ni < 0 || nj < 0 || ni >= w || nj >= h || g[ni][nj] == '.')continue;
int cost = (g[ci][cj] == g[ni][nj] ? 0 : 1);
if (dp[ni][nj] <= dp[ci][cj] + cost)continue;
dp[ni][nj] = dp[ci][cj] + cost;
if (cost == 0)q.push_front({ni,nj});
else q.push_back({ni,nj});
ans = max(ans,dp[ni][nj]);
}
}
cout<<ans + 1;
return 0;
}
