#include <bits/stdc++.h>
#define forr(i, a, b) for (int i = (a); i <= (b); i++)
#define ford(i, a, b) for (int i = (a); i >= (b); i--)
#define forf(i, a, b) for (int i = (a); i < (b); i++)
#define fi first
#define se second
#define pb push_back
#define all(v) v.begin(), v.end()
#define ll long long
#define ld long double
#define pii pair<int, int>
#define pll pair<ll, ll>
#define vi vector<int>
#define vii vector<pii>
#define mask(i) (1LL << (i))
#define bit(x, i) (((x) >> (i)) & 1)
#define bp __builtin_popcountll
#define file "test"
using namespace std;
const int base = 31;
const ll mod = 1e9 + 7;
const ll oo = 1e18;
const int N = 4005;
char a[N][N];
int d[N][N];
int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
int m, n;
cin >> m >> n;
forr(i, 1, m) forr(j, 1, n) cin >> a[i][j];
memset(d, 63, sizeof d);
deque<pii> dq;
dq.push_back({1, 1});
d[1][1] = 1;
int res = 0;
while (!dq.empty()){
pii u = dq.front();
dq.pop_front();
res = max(res, d[u.fi][u.se]);
forr(i, 0, 3){
int x = u.fi + dx[i], y = u.se + dy[i];
if (1 <= x && x <= m && 1 <= y && y <= n && a[x][y] != '.'){
if (d[u.fi][u.se] < d[x][y] && a[u.fi][u.se] == a[x][y]){
dq.push_front({x, y});
d[x][y] = d[u.fi][u.se];
}
else if (d[u.fi][u.se] + 1 < d[x][y] && a[u.fi][u.se] != a[x][y]){
dq.push_back({x, y});
d[x][y] = d[u.fi][u.se] + 1;
}
}
}
}
cout << res;
return 0;
}
