#include <bits/stdc++.h>
#define pll pair<long long, long long>
using namespace std;
char a[4005][4005];
long long dp[4005][4005], check[4005][4005];
deque<pll> q;
int main()
{
long long n, m, i, j, ans=0;
cin >> n >> m;
for (i=1; i<=n; i++)
{
for (j=1; j<=m; j++)
{
cin >> a[i][j];
};
};
q.push_back(make_pair(1, 1));
check[1][1]=dp[1][1]=1;
while (!q.empty())
{
i=q.front().first; j=q.front().second;
q.pop_front();
ans=max(ans, dp[i][j]);
if (i>1 && a[i-1][j]!='.' && !check[i-1][j])
{
check[i-1][j]=1;
if (a[i-1][j]==a[i][j]) {dp[i-1][j]=dp[i][j]; q.push_front(make_pair(i-1, j));}
else {dp[i-1][j]=dp[i][j]+1; q.push_back(make_pair(i-1, j));};
};
if (j>1 && a[i][j-1]!='.' && !check[i][j-1])
{
check[i][j-1]=1;
if (a[i][j-1]==a[i][j]) {dp[i][j-1]=dp[i][j]; q.push_front(make_pair(i, j-1));}
else {dp[i][j-1]=dp[i][j]+1; q.push_back(make_pair(i, j-1));};
};
if (i<n && a[i+1][j]!='.' && !check[i+1][j])
{
check[i+1][j]=1;
if (a[i+1][j]==a[i][j]) {dp[i+1][j]=dp[i][j]; q.push_front(make_pair(i+1, j));}
else {dp[i+1][j]=dp[i][j]+1; q.push_back(make_pair(i+1, j));};
};
if (j<m && a[i][j+1]!='.' && !check[i][j+1])
{
check[i][j+1]=1;
if (a[i][j+1]==a[i][j]) {dp[i][j+1]=dp[i][j]; q.push_front(make_pair(i, j+1));}
else {dp[i][j+1]=dp[i][j]+1; q.push_back(make_pair(i, j+1));};
};
};
cout << ans;
}
