#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define sz(s) (int)s.size()
#define bit(i, j) ((j >> i) & 1)
#define all(v) v.begin(), v.end()
#define taskname "file"
typedef long long ll;
const int N = 4e3;
int n, m, d[N + 5][N + 5];
char a[N + 5][N + 5];
bool vs[N + 5][N + 5];
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
struct node{
int val, x, y;
};
deque <node> dq;
void solve(){
cin >> n >> m;
for (int i = 1; i <= n; ++i)
for (int j = 1; j <= m; ++j)
cin >> a[i][j];
d[1][1] = 1;
vs[1][1] = true;
dq.push_back({1, 1, 1});
int ans = 0;
while (sz(dq)){
node x = dq.back();
dq.pop_back();
ans = max(ans, x.val);
for (int k = 0; k < 4; ++k){
int i = x.x + dx[k];
int j = x.y + dy[k];
if (i < 1 || i > n || j < 1 || j > m) continue;
if (vs[i][j]) continue;
if (a[i][j] == '.') continue;
vs[i][j] = true;
d[i][j] = x.val + (a[i][j] != a[x.x][x.y]);
if (d[i][j] != x.val) dq.push_front({d[i][j], i, j});
else dq.push_back({d[i][j], i, j});
}
}
cout << ans;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
// freopen(taskname".inp", "r", stdin);
// freopen(taskname".out", "w", stdout);
int tt = 1;
// cin >> tt;
while (tt--) solve();
}
