#include "bits/stdc++.h"
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define mod 1000000007
#define mod2 998244353
using namespace std;
using namespace __gnu_pbds;
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
bool inside(ll y, ll x, ll n, ll m)
{
return (y < n && y >= 0 && x < m && x >= 0);
}
void solve()
{
ll n, m;
cin >> n >> m;
vector<string> a(n);
for(int i = 0; i < n; ++i)
{
cin >> a[i];
}
vector<vector<ll>> dist(n, vector<ll>(m, -1));
vector<ll> yMove = {1, 0, -1, 0};
vector<ll> xMove = {0, 1, 0, -1};
dist[0][0] = 1;
deque<pair<ll, ll>> dq;
dq.push_front({0, 0});
while(!dq.empty())
{
auto [y, x] = dq.front(); dq.pop_front();
for(int i = 0; i < 4; ++i)
{
ll newY = y + yMove[i];
ll newX = x + xMove[i];
if(inside(newY, newX, n, m))
{
if(dist[newY][newX] != -1 || a[newY][newX] == '.') continue;
if(a[y][x] != a[newY][newX])
{
dist[newY][newX] = dist[y][x] + 1;
dq.push_back({newY, newX});
}else
{
dist[newY][newX] = dist[y][x];
dq.push_front({newY, newX});
}
}
}
}
ll ans = 0;
for(int i = 0; i < n; ++i)
{
for(int j = 0; j < m; ++j)
{
ans = max(ans, dist[i][j]);
// cout << dist[i][j] << " ";
}
// cout << "\n";
}
cout << ans << "\n";
}
int main(void)
{
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
solve();
}
