/*
#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 <= m && b <= m;
}
void djk()
{
dp[1][1] = 1;
deque<pii>dq;
dq.push_back({1,1});
int x,y,gox,goy;
while(!dq.empty())
{
x = dq.front().first;
y = dq.front().second;
dq.pop_front();
for(size_t i = 0; i < 4; ++i)
{
gox = x + dx[i];
goy = y + dy[i];
if(inbound(gox,goy) && a[gox][goy] != '.' && dp[gox][goy] == 0)
{
if(a[gox][goy] == a[x][y])
{
dp[gox][goy] = dp[x][y];
dq.push_front({gox,goy});
}
else
{
dp[gox][goy] = dp[x][y] + 1;
dq.push_back({gox,goy});
}
}
}
}
}
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();
}
}
