#include <bits/stdc++.h>
using namespace std;
#define vi vector<int>
#define vl vector<long long>
#define vii vector<pair<int,int>>
#define vll vector<pair<long long,long long>>
#define pb push_back
#define ll long long
#define ld long double
#define nl '\n'
#define boost ios::sync_with_stdio(false)
#define mp make_pair
#define se second
#define fi first
#define fore(i, y) for(int i = 0; i < y; i++)
#define forr(i,x,y) for(int i = x;i<=y;i++)
#define forn(i,y,x) for(int i = y; i >= x; i--)
#define all(v) v.begin(),v.end()
#define sz(v) v.size()
#define clr(v,k) memset(v,k,sizeof(v))
#define rall(v) v.rbegin() , v.rend()
#define pii pair<int,int>
#define pll pair<ll , ll>
const ll MOD = 1e9 + 7;
const ll INF = 1e9 + 1;
ll gcd(ll a , ll b) {return b ? gcd(b , a % b) : a ;} // greatest common divisor (PGCD)
ll lcm(ll a , ll b) {return a * (b / gcd(a , b));} // least common multiple (PPCM)
// HERE IS THE SOLUTION
vii coor = {{0 , 1} , {1 , 0} ,{-1 , 0} , {0 , -1}};
int main()
{
cin.tie(0);
cout.tie(0);
boost;
int n , m;
cin>>n>>m;
char grid[n][m];
fore(i , n)
{
fore(j , m)
{
cin>>grid[i][j];
}
}
int dist[n][m];
pii cur = {0 , 0};
fore(i , n)
{
fore(j , m)
{
dist[i][j] = INF;
}
}
dist[0][0] = 0;
deque<pii> dq;
dq.push_front(cur);
while(!dq.empty())
{
pii node = dq.front();
dq.pop_front();
for(auto p: coor)
{
int nx = p.fi + node.fi , ny = p.se + node.se;
if(nx < 0 || ny < 0 || nx>=n || ny>=m || grid[nx][ny] == '.')continue;
int w = 0;
if(grid[nx][ny] != grid[node.fi][node.se])
w = 1;
if(dist[nx][ny] > dist[node.fi][node.se] + w)
{
dist[nx][ny] = w + dist[node.fi][node.se];
if(w == 0)
dq.push_front({nx , ny});
else
dq.push_back({nx , ny});
}
}
}
int ans = 0;
fore(i , n)
{
fore(j , m)
{
if(grid[i][j] != '.')
ans = max(ans , dist[i][j]);
}
}
cout<<ans +1<<nl;
}
