#include <bits/stdc++.h>
#define ll long long
#define ff first
#define ss second
#define pb push_back
#define endl '\n'
using namespace std;
const int N=4e3 + 7;
const int mod = 1e9 + 7;
const ll inf = 1e12;
ll dist[N][N];
string s[N];
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
int n, m;
cin>>n>>m;
for(int i=0;i<n;i++){
cin>>s[i];
}
dist[0][0] = 1;
deque<pair<int, int>>q;
q.pb({0, 0});
ll ans = 0;
while(!q.empty()){
auto cur = q.front();q.pop_front();
ans = max(ans, dist[cur.ff][cur.ss]);
// cout<<cur.ff<<" "<<cur.ss<<" "<<dist[cur.ff][cur.ss]<<endl;
vector<pair<int, int>>dv = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
for(auto d: dv){
int x = cur.ff + d.ff;
int y = cur.ss + d.ss;
if(x < n && x >= 0 && y < m && y >= 0 && dist[x][y] == 0 && s[x][y] != '.'){
if(s[cur.ff][cur.ss] == s[x][y]){
dist[x][y] = dist[cur.ff][cur.ss];
q.push_front({x, y});
} else {
dist[x][y] = dist[cur.ff][cur.ss] + 1;
q.push_back({x, y});
}
}
}
}
cout<<ans<<endl;
/*/
RRRRFR
RRF
RF
RR
*/
}
