#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#pragma GCC optimize("O3,unroll-all-loops")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define all(v) v.begin(), v.end()
#define pb push_back
#define ss second
#define ff first
#define vt vector
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef pair<int, int> pii;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
const int inf = 1e9;
const int mod = 1e9+7;
const int maxn = 4e3 + 2;
char a[maxn][maxn];
bool was[maxn][maxn];
int dp[maxn][maxn];
deque<pii> q;
void go(int x, int y, char s, int wt){
if(a[x][y] != s)dp[x][y] = wt + 1, q.push_back({x, y});
else dp[x][y] = wt, q.push_front({x, y});
was[x][y] = 1;
}
void solve() {
int n, m;
cin >> n >> m;
for(int i = 1; i <= n; i++){
was[i][0] = was[i][m + 1] = 1;
for(int j = 1; j <= m; j++){
cin >> a[i][j];
if(a[i][j] == '.')was[i][j] = 1;
}
}
for(int i = 1; i <= m; i++)was[0][i] = was[n + 1][i] = 1;
int ans = 1;
char s = a[n][m];
go(n, m, s, 1);
while(!q.empty()){
pii nw = q.front();
q.pop_front();
int x = nw.ff, y = nw.ss;
ans = dp[x][y];
s = a[x][y];
if(!was[x - 1][y])go(x - 1, y, s, ans);
if(!was[x + 1][y])go(x + 1, y, s, ans);
if(!was[x][y - 1])go(x, y - 1, s, ans);
if(!was[x][y + 1])go(x, y + 1, s, ans);
}
cout << ans;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int times = 1;
//cin >> times;
for(int i = 1; i <= times; i++) {
solve();
}
return 0;
}
