// barkolorious - 01 December 2024
// in god, do we trust?
#include <bits/stdc++.h>
using namespace std;
#define FIN(x) freopen(x ".in", "r", stdin)
#define FOUT(x) freopen(x ".out", "w", stdout)
#define int long long
#define pb push_back
#define fr first
#define sc second
#define __ << " " <<
const int N = 4e3 + 5;
char snow[N][N];
int dist[N][N], vis[N][N];
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
int w, h;
bool check (int x, int y) {
return (1 <= x && x <= w) && (1 <= y && y <= h);
}
void solve () {
cin >> h >> w;
for (int y = 1; y <= h; y++) {
for (int x = 1; x <= w; x++) {
cin >> snow[x][y];
}
}
deque<pair<int, int>> dq;
dq.push_front({1, 1});
dist[1][1] = 1;
vis[1][1] = true;
int ans = 1;
while (!dq.empty()) {
int x = dq.front().fr, y = dq.front().sc;
dq.pop_front();
ans = max(ans, dist[x][y]);
// cout << x __ y << endl;
for (int i = 0; i < 4; i++) {
int xx = x + dx[i], yy = y + dy[i];
if (!check(xx, yy)) continue;
if (snow[xx][yy] == '.') continue;
if (vis[xx][yy]) continue;
vis[xx][yy] = true;
if (snow[x][y] == snow[xx][yy]) {
dist[xx][yy] = dist[x][y];
dq.push_front({xx, yy});
} else {
dist[xx][yy] = dist[x][y] + 1;
dq.push_back({xx, yy});
}
}
}
cout << ans << endl;
}
/*
-- Sample 1 --
Input:
5 8
FFR.....
.FRRR...
.FFFFF..
..RRRFFR
.....FFF
Output:
2
*/
/*
g++ -std=c++17 -O2 -Wall -DLOCAL "C:\Users\LENOVO\Desktop\BARKIN\Genel\Programming\Competitive\Questions\Olympiads\BOI13\BOI13_tracks.cpp" -o _run
*/
int32_t main () {
#ifndef LOCAL
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
#endif
#ifdef LOCAL
clock_t __START__ = clock();
FILE* __FILE_IN__ = FIN("C:/Users/LENOVO/Desktop/BARKIN/Genel/Programming/Competitive/_run");
FILE* __FILE_OUT__ = FOUT("C:/Users/LENOVO/Desktop/BARKIN/Genel/Programming/Competitive/_run");
#endif
solve();
#ifdef LOCAL
fclose(__FILE_IN__);
fclose(__FILE_OUT__);
cerr << "Executed in: " << fixed << setprecision(3) << (double) (clock() - __START__) / CLOCKS_PER_SEC << "seconds" << endl;
#endif
return 0;
}
