#include "bits/stdc++.h"
using namespace std;
#define ff first
#define ss second
#define all(v) v.begin(), v.end()
#define ll long long
#define pb push_back
#define pii pair<int, int>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define tr(i, c) for(auto i = c.begin(); i != c.end(); ++i)
#define wr puts("----------------")
template<class T>bool umin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool umax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
const int N = 4e3+5;
int dis[N][N], dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1};
bool vis[N][N];
char c[N][N];
int main(){
int n, m;
scanf("%d%d", &n, &m);
for(int i = 1; i <= n; ++i)
for(int j = 1; j <= m; ++j)
scanf(" %c", &c[i][j]), vis[i][j]=(c[i][j]=='.'?1:0);
auto is = [&](int x, int y) -> bool {
return (x>=1 and x<=n and y>=1 and y<=m and !vis[x][y]);
};
deque<pii> dq;
dq.pb({1, 1}), dis[1][1] = 1, vis[1][1] = 1;
int answer = 0;
while(!dq.empty()){
pii P = dq.front();
dq.pop_front(), umax(answer, dis[P.ff][P.ss]);
for(int ad = 0; ad < 4; ++ad){
int x = P.ff+dx[ad], y = P.ss+dy[ad];
if(!is(x, y))
continue;
if(c[x][y]==c[P.ff][P.ss])
dis[x][y]=dis[P.ff][P.ss], vis[x][y]=1, dq.push_front({x, y});
else
dis[x][y]=dis[P.ff][P.ss]+1, vis[x][y]=1, dq.pb({x, y});
}
}
printf("%d\n", answer);
return 0;
}
