#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define X first
#define Y second
//const ll mod = 1000000007;
const ll mod = 998244353;
int dp[4001][4001];
void solve()
{
ll n, m;
cin >> n >> m;
vector<string> s(n);
for (int i=0;i<n;i++) cin >> s[i];
deque<int> Q;
Q.push_back(0);
for (int i=0;i<n;i++)
{
for (int j=0;j<m;j++) dp[i][j] = mod;
}
dp[0][0] = 0;
vector<int> was(n*m);
vector<int> dx = {1,-1,0,0};
vector<int> dy = {0,0,1,-1};
while (Q.size()>0)
{
int p = Q.front();
Q.pop_front();
if (was[p]==1) continue;
was[p] = 1;
int x = p/m;
int y = p-m*x;
for (int d=0;d<4;d++)
{
int x2 = x+dx[d];
int y2 = y+dy[d];
if (x2>=n or x2<0 or y2>=m or y2<0 or s[x2][y2]=='.') continue;
int W = dp[x][y];
int F = 0;
if (s[x][y]!=s[x2][y2]) F = 1;
if (dp[x2][y2]>W+F)
{
dp[x2][y2] = W+F;
if (F==0) Q.push_front(x2*m+y2);
else Q.push_back(x2*m+y2);
}
}
}
int A = 0;
for (int i=0;i<n;i++)
{
for (int j=0;j<m;j++)
{
if (dp[i][j]<mod) A = max(A,dp[i][j]);
}
}
cout << A+1 << "\n";
}
int main()
{
ios_base::sync_with_stdio(false);
ll T;
T = 1;
//cin >> T;
while (T--) solve();
}
