#include <bits/stdc++.h>
using namespace std;
struct pos
{
int x, y, len;
pos(int x, int y, int len)
{
this->x = x;
this->y = y;
this->len = len;
}
};
int dx[] = {0, 0, -1, 1};
int dy[] = {-1, 1, 0, 0};
int n,m,ans;
char a[4005][4005];
int d[4005][4005];
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cin>>n>>m;
for(int i=1; i<=n; i++)
for(int j=1; j<=m; j++)
cin>>a[i][j];
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
d[i][j] = -1;
deque<pos> q;
q.push_back(pos(1, 1, 1));
while(!q.empty())
{
int x = q.front().x;
int y = q.front().y;
int len = q.front().len;
q.pop_front();
if(d[x][y] != -1)
continue;
d[x][y] = len;
ans = len;
for(int i=0; i<4; i++)
{
int nx = x + dx[i];
int ny = y + dy[i];
if(nx < 1 || nx > n || ny < 1 || ny > m || d[nx][ny] != -1 || a[nx][ny] == '.')
continue;
if(a[x][y] == a[nx][ny])
q.push_front(pos(nx, ny, len));
else
q.push_back(pos(nx, ny, len+1));
}
}
cout<<ans;
return 0;
}
