#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
using ll = long long;
using ld = long double;
#define pb push_back
#define sz size()
typedef pair<int, int> pii;
typedef pair<int, pii> piii;
const int maxn = 4002, inf = 2e7;
char maze[maxn][maxn];
int d[maxn][maxn];
vector<pii> movements(4);
struct comp{
bool operator() (piii a, piii b){
return a.first > b.first;
}
};
void initializeMovements(){
movements[0] = {0, -1};
movements[1] = {0, 1};
movements[2] = {-1, 0};
movements[3] = {1, 0};
}
void BFS(int n, int m){
priority_queue<piii, vector<piii>, comp> pq; pq.push({0, {n-1, m-1}});
d[n-1][m-1] = 1;
while(!pq.empty()){
int ux = pq.top().second.second, uy = pq.top().second.first;
pq.pop();
for(int i = 0; i < 4; i++){
int vx = ux + movements[i].second, vy = uy + movements[i].first;
if(vx < 0 || vy >= m || vy < 0 || vy >= n || maze[vy][vx] == '.') continue;
int add = 0;
if(maze[uy][ux] != maze[vy][vx]) add++;
if(d[vy][vx] > d[uy][ux] + add){
d[vy][vx] = d[uy][ux] + add;
pq.push({d[vy][vx], {vy, vx}});
}
}
}
}
void solver(){
initializeMovements();
int n, m; cin>>n>>m;
for(int i = 0; i < n; i++) cin>>maze[i];
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
d[i][j] = inf;
}
}
BFS(n, m);
int ans = 0;
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
if(maze[i][j] == '.') continue;
ans = max(ans, d[i][j]);
}
}
cout<<ans<<endl;
}
int main(){
ios_base::sync_with_stdio(0);cin.tie(NULL);
int t = 1;
// cin>>t;
while(t--){
solver();
}
return 0;
}
