// Src : Vux2Code
/* Note :
*/
#include <bits/stdc++.h>
#define fi first
#define se second
#define pusb push_back
#define popb pop_back
#define pusf push_front
#define popf pop_front
using namespace std;
// template <typename T> void vout(T s){ cout << s << endl; exit(0);}
typedef long long ll;
typedef long double ld;
typedef pair <ll, ll> pll;
const ll maxN = 4e3 + 5, maxLog = 20, inf64 = 1e18, inf32 = 1e9, mod = 1e9 + 7;
void maxi (ll &x, ll y) {x = max (x, y);}
void mini (ll &x, ll y) {x = min (x, y);}
/* ---------HASHING-------- */
// const base = 31, mod2 = 1e9 + 9;
/* ---------BITMASK-------- */
// ll count (ll x) {return __builtin_popcountll (x);}
// ll fst (ll x) {return 63 - __builtin_clzll (x);}
// ll last (ll x) {return __builtin_ctzll (x);}
// bool bit (ll x, ll y) {return ((x >> y) & 1);}
pll adj [] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
ll t = 1;
ll n, m, d [maxN] [maxN];
char a [maxN] [maxN];
deque <pll> q;
char c (pll x) {
return a [x. fi] [x. se];
}
bool outBoard (pll x) {
return x. fi < 1 || x. fi > n || x. se < 1 || x. se > m || a [x. fi] [x. se] == '.';
}
void solve () {
cin >> n >> m;
for (int i = 1; i <= n; i ++) {
for (int j = 1; j <= m; j ++) {
cin >> a [i] [j];
}
}
memset (d, 0x3f, sizeof d);
d [1] [1] = 1;
q. pusb ({1, 1});
ll ans = 0;
while (!q. empty ()) {
pll tmp = q. front ();
// cerr << tmp. fi << ' ' << tmp. se << ' ' << d [tmp. fi] [tmp. se] << '\n';
maxi (ans, d [tmp. fi] [tmp. se]);
q. popf ();
for (pll i : adj) {
pll nx = {tmp. fi + i. fi, tmp. se + i. se};
if (outBoard (nx)) continue;
if (c (nx) == c (tmp)) {
if (d [nx. fi] [nx. se] > d [tmp. fi] [tmp. se]) {
d [nx. fi] [nx. se] = d [tmp. fi] [tmp. se];
q. pusf (nx);
}
}
else {
if (d [nx. fi] [nx. se] > d [tmp. fi] [tmp. se] + 1) {
d [nx. fi] [nx. se] =d [tmp. fi] [tmp. se] + 1;
q. pusb (nx);
}
}
}
}
cout << ans;
}
int main () {
ios::sync_with_stdio (0);
cin.tie (0);
cout.tie (0);
// #define TASK "E:/Code/CP/task"
// if (fopen (TASK".inp", "r")) {
// freopen (TASK".inp", "r", stdin);
// freopen (TASK".out", "w", stdout);
// }
//cin >> t;
while (t--) solve ();
}
