#include <bits/stdc++.h>
using namespace std;
//#pragma GCC optimize("Ofast")
//#pragma GCC target("avx,avx2,fma")
#define ll long long
#define pb push_back
#define pf push_front
#define pob pop_back
#define pof pop_front
#define vi vector<int>
#define rep(i, n) for (int i = 0; i < n; i++)
#define w(t) \
int t; \
cin >> t; \
while (t--)
#define ff first
#define ss second
#define in(azz, sz) \
for (int ix = 0; ix < sz; ix++) \
cin >> azz[ix];
#define in2d(azz, row, column) rep(i, row) rep(j, column) cin >> azz[i][j];
#define out2d(azz, row, column) \
rep(i, row) \
{ \
rep(j, column) cout << azz[i][j] << " "; \
cout << "\n" \
};
#define out(azz, sz) \
for (int ix = 0; ix < sz; ix++) \
{ \
cout << azz[ix] << " "; \
} \
cout << endl
#define mii map<int, int>
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define mod 1000000007
#define endl '\n'
#define SORT(a) sort(a.begin(), a.end())
#define REVERSE(a) reverse(a.begin(), a.end())
#define ALL(a) a.begin(), a.end()
#define deb(x) cout << #x << "=" << x << endl
#define deb2(x, y) cout << #x << "=" << x << "," << #y << "=" << y << endl
#define ps(x, y) fixed << setprecision(y) << x
#define mp make_pair
#define all(vx) vx.begin(), vx.end()
#define maxv(azz) max_element(all(azz)) - azz.begin() //return index of max element of vector;
#define minv(azz) min_element(all(azz)) - azz.begin() //return index of min element of vector;
#define maxa(azz) max_element(azz, azz + n) - azz //return index of max element of array, n==size of array;
#define mina(azz) min_element(azz, azz + n) - azz //return index of min element of array, n==size of array;
#define isort(azz) is_sorted(all(azz)) //check if elements are sorted;
#define setpres cout.precision(numeric_limits<double>::max_digits10);
#define rev(vx) reverse(all(vx))
#define fastio \
ios_base::sync_with_stdio(0); \
cin.tie(0); \
cout.tie(0);
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef set<int> seti;
#define am(a, b) MOD(MOD(a) + MOD(b))
#define mm(a, b) MOD(MOD(a) * MOD(b))
#define yes cout << "YES" << endl;
#define no cout << "NO" << endl;
const ll INF = 1000000007;
ll MOD(ll a)
{
a = a % INF;
while (a < 0)
a += INF;
return a;
}
ll binpow(ll a, ll b)
{
ll res = 1;
while (b > 0)
{
if (b & 1)
res = mm(res, a);
a = mm(a, a);
b >>= 1;
}
return res;
}
ll modInverse(ll a)
{
return binpow(a, INF - 2);
}
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
DON'T MAKE CHANGES BEFORE THIS LINE!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
#define int ll //use only if needed;
int depth[5000][5000];
int n = 4000, m = 4000;
int ans = -1;
int dx[4]{1, -1, 0, 0}, dy[4]{0, 0, 1, -1};
string snow[4000];
bool inside(int x, int y)
{
return (x > -1 && x < n && y > -1 && y < m && snow[x][y] != '.');
}
void tosolve()
{
cin >> n >> m;
rep(i, n) cin >> snow[i];
deque<pair<int, int>> q;
q.push_back({0, 0});
depth[0][0] = 1;
while (q.size())
{
pair<int, int> c = q.front();
q.pop_front();
ans = max(ans, depth[c.first][c.second]);
for (int i = 0; i < 4; i++)
{
int x = c.first + dx[i], y = c.second + dy[i];
if (inside(x, y) && depth[x][y] == 0)
{
if (snow[x][y] == snow[c.first][c.second])
{
depth[x][y] = depth[c.first][c.second];
q.push_front({x, y});
}
else
{
depth[x][y] = depth[c.first][c.second] + 1;
q.push_back({x, y});
}
}
}
}
cout << ans << endl;
return;
}
int32_t main()
{
fastio
{
tosolve();
}
return 0;
}
/*
███╗░░░███╗██╗████████╗██╗░░██╗██╗██╗░░░░░
████╗░████║██║╚══██╔══╝██║░░██║██║██║░░░░░
██╔████╔██║██║░░░██║░░░███████║██║██║░░░░░
██║╚██╔╝██║██║░░░██║░░░██╔══██║██║██║░░░░░
██║░╚═╝░██║██║░░░██║░░░██║░░██║██║███████╗
╚═╝░░░░░╚═╝╚═╝░░░╚═╝░░░╚═╝░░╚═╝╚═╝╚══════╝
* Author : mithilshah23
* Website : Oj
* Problem : track in the snow
* Time : 21-08-2021 11:00:52
* Lang : GNU C++17
*/
