#include <bits/stdc++.h>
// #pragma GCC optimize("Ofast,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
using namespace std;
/*
two puddles of the same type are intersected by one with connection to start, then its all 2 animals only
começo no início
- tudo q eu percorrer é 1 bicho só, todos os diferentes adjacentes a ele são do mesmo bicho só, e assim por diante
*/
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count()); // overclock random
typedef pair<int,int> pii;
typedef pair<long long, long long> pll;
typedef pair<double, double> pdd;
const int MAXN = 4e3+12;
char g[MAXN][MAXN];
int d[MAXN][MAXN], aux[4] = {1,-1, 0, 0};
signed main(){
std::ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
// freopen("test.in", "r", stdin);
// freopen("test.out", "w", stdout);
// cout << fixed << setprecision(12);
int n, m;
cin >> n >> m;
for (int i=1;i<=n;i++) for (int j=1;j<=m;j++){
cin >> g[i][j];
d[i][j] = 1e9;
if (g[i][j] == '.') d[i][j] = -1;
}
priority_queue<pair<int, pii>, vector<pair<int, pii>>, greater<>> q;
q.push({1, {1,1}});
d[1][1] = 1;
int ans=1;
while (!q.empty()){
auto u = q.top();
q.pop();
if (u.first != d[u.second.first][u.second.second]) continue;
ans = max(ans, u.first);
pii x = u.second;
char t = g[x.first][x.second];
for (int a=0,b=3;a<4;a++,b--){
int ni = x.first+aux[a],nj=x.second+aux[b];
if (d[ni][nj] == -1) continue;
int nd = u.first + (t != g[ni][nj]);
if (d[ni][nj] <= nd) continue;
d[ni][nj] = nd;
q.push({nd, {ni,nj}});
}
}
cout << ans << "\n";
return 0;
}
