#include<bits/stdc++.h>
using namespace std;
const int maxN = (int)4e3 + 2;
const int maxM = (int)4e3 + 2;
char c[maxN][maxM];
int dx[4] = {0,0,1,-1},dy[4] = {1,-1,0,0};
int dist[maxN][maxM];
int main()
{
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int n,m;
cin >> n >> m;
for(int i=1;i<=n;++i) for(int j=1;j<=m;++j) cin >> c[i][j],dist[i][j] = INT_MAX - 10;
dist[1][1] = 1;
deque<array<int,2>> dq;
dq.push_front({1,1});
while(dq.size())
{
int x = dq.front()[0];
int y = dq.front()[1];
dq.pop_front();
for(int i=0;i<4;++i)
{
int nx = x + dx[i],ny = y + dy[i];
if(nx >= 1 && nx <= n && ny >= 1 && ny <= m)
if(c[nx][ny] != '.')
{
int cost = 0;
if(c[nx][ny] != c[x][y]) ++cost;
if(dist[nx][ny] > dist[x][y] + cost)
{
dist[nx][ny] = dist[x][y] + cost;
if(!cost) dq.push_front({nx,ny});
else dq.push_back({nx,ny});
}
}
}
}
int ans = 0;
for(int i=1;i<=n;++i) for(int j=1;j<=m;++j) if(c[i][j] != '.')ans = max(ans,dist[i][j]);
cout << ans;
return 0;
}
