#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <cmath>
using namespace std;
using ll = long long;
const int MAXN = 4e3;
const int INF = 2e9;
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};
string T[1 + MAXN];
int dist[1 + MAXN][1 + MAXN];
int n, m;
bool out( int i, int j ) {
return 1 > i || 1 > j || n < i || m < j;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
for ( int i = 1; i <= n; ++i ) {
cin >> T[i];
T[i] = '#' + T[i];
for ( int j = 1; j <= m; ++j ) {
dist[i][j] = INF;
}
}
deque<pair<int, int>> dq;
dq.push_back({1, 1});
dist[1][1] = 1;
int res = 1;
while ( !dq.empty() ) {
auto [i, j] = dq.front();
dq.pop_front();
res = max(res, dist[i][j]);
for ( int d = 0; d < 4; ++d ) {
int ni = i + dx[d], nj = j + dy[d];
if ( out(ni, nj) || T[ni][nj] == '.' ) continue;
int cost = T[ni][nj] != T[i][j];
if ( dist[ni][nj] > dist[i][j] + cost ) {
dist[ni][nj] = dist[i][j] + cost;
if ( cost == 0 ) {
dq.push_front({ni, nj});
} else {
dq.push_back({ni, nj});
}
}
}
}
cout << res << "\n";
return 0;
}
