#include <bits/stdc++.h>
#define MAX 4005
#define PII pair<int,int>
using namespace std;
char mat[MAX][MAX];
int bfs[MAX][MAX];
int dl[]={-1,0,1,0};
int dc[]={0,1,0,-1};
int main()
{
int n,m;
cin>>n>>m;
int i,j;
for(i=1;i<=n;++i)
for(j=1;j<=m;++j)
{
cin>>mat[i][j];
bfs[i][j]=INT_MAX;
}
bfs[1][1]=1;
deque<PII>deq;
deq.push_front({1,1});
while(!deq.empty())
{
PII nou=deq.front();
int l=nou.first;
int c=nou.second;
deq.pop_front();
for(i=0;i<4;++i)
{
int lnou=l+dl[i];
int cnou=c+dc[i];
int pret=bfs[l][c]+(mat[l][c]!=mat[lnou][cnou]);
if(isalpha(mat[lnou][cnou]) && pret<bfs[lnou][cnou])
{
bfs[lnou][cnou]=pret;
if(mat[l][c]==mat[lnou][cnou])
deq.push_front({lnou,cnou});
else
deq.push_back({lnou,cnou});
}
}
}
int answer=-1;
for(i=1;i<=n;++i)
for(j=1;j<=m;++j)
if(isalpha(mat[i][j]))
answer=max(answer,bfs[i][j]);
cout<<answer;
return 0;
}
