#include<bits/stdc++.h>
#define fi first
#define se second
using namespace std;
char meadow[4004][4004];
int num[4004][4004] = {0};
int main() {
int row, column;
cin >> row >> column;
for(int i=1; i<=row; i++) {
for(int j=1; j<=column; j++) {
cin >> meadow[i][j];
}
}
int animals = 1;
queue<pair<int,int>>q;
stack<pair<int,int>>other;
q.push({1,1});
num[1][1] = 1;
while(!q.empty()) {
int bar = q.front().fi;
int kol = q.front().se;
q.pop();
animals = max(animals, num[bar][kol]);
//atas
if(bar-1>=1 && num[bar-1][kol]==0) {
if(meadow[bar-1][kol] == meadow[bar][kol]) {
q.push({bar-1,kol});
num[bar-1][kol] = num[bar][kol];
} else
if(meadow[bar-1][kol] != '.') {
other.push({bar-1,kol});
num[bar-1][kol] = num[bar][kol]+1;
}
}
//bawah
if(bar+1<=row && num[bar+1][kol]==0) {
if(meadow[bar+1][kol] == meadow[bar][kol]) {
q.push({bar+1,kol});
num[bar+1][kol] = num[bar][kol];
} else
if(meadow[bar+1][kol] != '.') {
other.push({bar+1,kol});
num[bar+1][kol] = num[bar][kol]+1;
}
}
//kiri
if(kol-1>=1 && num[bar][kol-1]==0) {
if(meadow[bar][kol-1] == meadow[bar][kol]) {
q.push({bar,kol-1});
num[bar][kol-1] = num[bar][kol];
} else
if(meadow[bar][kol-1] != '.') {
other.push({bar,kol-1});
num[bar][kol-1] = num[bar][kol]+1;
}
}
//kanan
if(kol+1<=column && num[bar][kol+1]==0) {
if(meadow[bar][kol+1] == meadow[bar][kol]) {
q.push({bar,kol+1});
num[bar][kol+1] = num[bar][kol];
} else
if(meadow[bar][kol+1] != '.') {
other.push({bar,kol+1});
num[bar][kol+1] = num[bar][kol]+1;
}
}
if(q.empty()==true) {
while(!other.empty()) {
q.push(other.top());
other.pop();
}
}
}
cout << animals << endl;
return 0;
}
