#include <bits/stdc++.h>
using namespace std;
const long long INFll = (long long) 1e18 + 10;
const int INFii = (int) 1e9 + 10;
typedef long long ll;
typedef int ii;
typedef long double dbl;
#define endl '\n'
#define sc second
#define fr first
#define mp make_pair
#define pb push_back
#define all(x) x.begin(), x.end()
#define maxn 4400
ii n, m;
char c[maxn][maxn];
ii dx[4] = {0,0,1,-1};
ii dy[4] = {1,-1,0,0};
int main() {
ios::sync_with_stdio(false); cin.tie(0);
//freopen("in.in", "r", stdin);
//freopen("out.out", "w", stdout);
cin >> n >> m;
for(ii i = 1; i <= n; i++) {
c[i][0] = c[i][m+1] = '.';
string s;
cin >> s;
for(ii j = 1; j <= m; j++) {
c[i][j] = s[j-1];
}
}
for(ii j = 1; j <= m; j++) c[0][j] = c[n+1][j] = '.';
queue<pair<ii,ii>> q1, q2;
ii ans = 0;
q2.push(mp(1,1));
while(q1.size() + q2.size()) {
if(q1.empty()) {
ans++;
swap(q1,q2);
}
ii x = q1.front().fr;
ii y = q1.front().sc;
q1.pop();
if(c[x][y] == '.') continue;
for(ii i = 0; i < 4; i++) {
ii x1 = x + dx[i];
ii y1 = y + dy[i];
if(c[x1][y1] == c[x][y]) {
q1.push(mp(x1,y1));
}
else if(c[x1][y1] != '.') {
q2.push(mp(x1,y1));
}
}
c[x][y] = '.';
}
cout << ans << endl;
}
