#include<bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
#define inin int
#define vi vector<int>
#define all(x) x.begin(), x.end()
/*
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<class T> using oset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
*/
const inin N=1e3+2, M=3e5+10, mod=1e9+7;
bool com(vector<int> a, vector<int> b){
return abs(a[1]-a[0])<abs(b[1]-b[0]);
}
vector<int> mx = {1, -1, 0, 0}, my = {0, 0, 1, -1};
int h, w;
const int n = 4010;
vector<vector<char>> a(n, vector<char>(n, '.'));
vector<vector<int>> depth(n, vector<int>(n, 0));
bool isinside(int x, int y){
return (x>=0 && y>=0 && x<h && y<w && a[x][y]!='.');
}
int main(){
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
cout<<setprecision(15)<<fixed;
cin>>h>>w;
for(int i=0; i<h; i++){
for(int j=0; j<w; j++){
cin>>a[i][j];
}
}
deque<pair<int, int>> d;
d.push_back({0, 0});
depth[0][0] = 1;
int ans = 0;
while(!d.empty()){
int x = d.front().first, y = d.front().second;
d.pop_front();
ans = max(ans, depth[x][y]);
for(int i=0; i<4; i++){
int xn = x+mx[i], yn = y+my[i];
if(isinside(xn, yn) && depth[xn][yn] == 0){
if(a[x][y] == a[xn][yn]){
depth[xn][yn] = depth[x][y];
d.push_front({xn, yn});
}else{
depth[xn][yn] = depth[x][y]+1;
d.push_back({xn, yn});
}
}
}
}
cout<<ans<<endl;
}
