/*
#ifndef ONLINE_JUDGE
#include "AkbarKING.h" // aska geldi akbarking.h
#else
#define debug(...)
#define debugArr(...)
#define debugG(...)
#endif
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/hash_policy.hpp>
#define int long long
#define $AzH_TxdmN$ ios_base::sync_with_stdio(0);cin.tie(nullptr);cout.tie(nullptr);
#pragma GCC target("sse,sse2,sse3,ssse3,popcnt,abm,mmx,tune=native")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("fast-math")
#define ep emplace_back
#define pb push_back
#define pii pair<int,int>
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define heap pii, vector<pii>, less<pii>
using namespace std;
using namespace __gnu_pbds;
template <typename T>
using __indexed_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template <typename T>
using __indexed_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;
const int sz = 4e3 +9;
const int LOG = 63;
const int MOD = 1e9+7;
const int INF = 1e18;
int dx[] = {-1,0,1,0};
int dy[] = {0,1,0,-1};
int dp[sz][sz];
bool used[sz][sz];
char a[sz][sz];
int n,m;
bool inbound(const int &a, const int &b)
{
return 1 <= a && 1 <= b && a <= n && b <= m;
}
void djk()
{
dp[1][1] = 1;
priority_queue<heap> q;
q.push({ 1, 1 });
while(!q.empty())
{
int i, j;
tie(i, j) = q.top();
q.pop();
for(int t = 0; t <= 3; t ++)
{
int u = i + dx[t], v = j + dy[t];
if(inbound(u, v) && a[u][v] != '.' && dp[u][v] == 0)
{
if(a[u][v] == a[i][j])
{
dp[u][v] = dp[i][j];
q.push({ u, v });
}
else
{
dp[u][v] = dp[i][j] + 1;
q.push({ u, v });
}
}
}
}
}
void solve()
{
cin>>n>>m;
for (int i = 1; i <= n; ++i)
{
for (int j = 1; j <= m; ++j)
{
cin>>a[i][j];
}
}
djk();
int res = 0;
for (int i = 1; i <= n; ++i)
{
for (int j = 1; j <= m; ++j)
{
res = max(res,dp[i][j]);
}
}
cout<<res<<'\n';
}
signed main()
{
$AzH_TxdmN$
int t = 1;
//cin>>t;
while (t--)
{
solve();
}
}
