#include <bits/stdc++.h>
#define ll long long
#define ull unsigned ll
#define pb push_back
#define pa pair<int, int>
#define pall pair<ll, int>
#define fi first
#define se second
#define TASK "test"
#define all(x) x.begin(), x.end()
using namespace std;
template<typename T1, typename T2> bool mini (T1 &a, T2 b) {if(a > b) a = b; else return 0; return 1;}
template<typename T1, typename T2> bool maxi (T1 &a, T2 b) {if(a < b) a = b; else return 0; return 1;}
const int MOD = 1e9 + 7;
const int LOG = 20;
const int maxn = 4e3 + 7;
const ll oo = 1e17 + 69;
int n, m, f[maxn][maxn];
char a[maxn][maxn];
pa d[] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
void bfs() {
deque<pa> q;
memset(f, 0, sizeof f);
f[0][0] = 1;
q.push_front({0, 0});
int ans = 0;
while(!q.empty()) {
int u = q.front().fi;
int v = q.front().se;
q.pop_front();
maxi(ans, f[u][v]);
for(int k = 0; k < 4; k++) {
int x = u + d[k].fi;
int y = v + d[k].se;
if(x < 0 || x == n || y < 0 || y == m || f[x][y] || a[x][y] == '.') continue;
int w = (a[u][v] != a[x][y]);
f[x][y] = f[u][v] + w;
if(w) q.pb({x, y});
else q.push_front({x, y});
}
}
cout<<ans;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
//freopen(TASK".inp", "r", stdin);
//freopen(TASK".out", "w", stdout);
cin>>n>>m;
for(int i = 0; i < n; i++)
for(int j = 0; j < m; j++) cin>>a[i][j];
bfs();
return 0;
}
