#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define MOD 998244353
const int N = 4002, cd[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
ll n, m, d[N][N], mx = 1;
char c[N][N];
deque<pair<ll, ll>> q;
void solve()
{
cin >> n >> m;
for (int i = 0; i < n; i++)
cin >> c[i];
d[0][0] = 1;
q.push_back({0, 0});
while (!q.empty())
{
ll x, y;
x = q.front().first;
y = q.front().second;
q.pop_front();
mx = max(mx, d[x][y]);
for (int i = 0; i < 4; i++)
{
ll nx = x + cd[i][0], ny = y + cd[i][1];
if (nx < 0 or nx >= n or ny < 0 or ny >= m or c[nx][ny] == '.' or d[nx][ny])
{
continue;
}
if (c[nx][ny] == c[x][y])
{
d[nx][ny] = d[x][y];
q.push_front({nx, ny});
}
else
{
d[nx][ny] = d[x][y] + 1;
q.push_back({nx, ny});
}
}
}
cout << mx << '\n';
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
ll t = 1;
// cin >> t;
for (ll i = 1; i <= t; i++)
{
solve();
}
}
