#include<bits/stdc++.h>
using namespace std;
#ifdef DEBUG
auto&operator <<(auto& o, pair<auto, auto> p) {return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator <<(auto& o, auto x)->decltype(x.end(), o) {o<<"{"; for(auto v : x) o<<v<<", "; return o<<"}";}
#define debug(X) cout<<"["#X"]"<<X<<endl;
#else
#define debug(X) {}
#endif
#define int long long
int32_t main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int n, m;
cin>>n>>m;
vector brd(n+2, vector(m+2, '.'));
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)
cin>>brd[i][j];
vector<int> dx = {1, -1, 0, 0};
vector<int> dy = {0, 0, 1, -1};
vector dist(n+2, vector(m+2, (int)1e9));
deque<pair<int, int> > q;
q.push_back({1, 1});
dist[1][1] = 1;
while(!q.empty())
{
auto a = q.front();
q.pop_front();
for(int i=0;i<4;i++)
{
int nx = a.first + dx[i], ny = a.second + dy[i];
if(brd[nx][ny] == '.') continue;
int d = 0;
if(brd[nx][ny] != brd[a.first][a.second]) d = 1;
if(dist[nx][ny] > dist[a.first][a.second] + d)
{
dist[nx][ny] = dist[a.first][a.second]+d;
if(d == 0) q.push_front({nx, ny});
if(d == 1) q.push_back({nx, ny});
}
}
}
debug(dist);
int res = 1;
for(auto v : dist)
for(auto u : v)
if(u != 1e9) res = max(res, u);
cout<<res;
}
