#include <bits/stdc++.h>
#define ll long long
#define sti string
#define vt vector
#define INF ((int) 1e9)
#define MOD 1000000007
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define dbg(x) cerr << #x << " = " << x << '\n';
#define bit(mask, i) ((mask >> i) & 1)
#define fi first
#define sc second
#define MAXXTEST 100
#define MAXN 4000
#define MAXNTEST 100
#define SOTEST 100
using namespace std;
const sti name = "";
inline void stress_test ()
{
}
inline void file ()
{
freopen((name + ".inp").c_str(), "r", stdin);
freopen((name + ".out").c_str(), "w", stdout);
}
char a[MAXN + 5][MAXN + 5];
int D[MAXN + 5][MAXN + 5],
dx[] = {0, 0, -1, 1},
dy[] = {1, -1, 0, 0},
H, W;
inline bool check(int x, int y)
{
return 1 <= x && x <= H && 1 <= y && y <= W && a[x][y] != '.';
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
cin >> H >> W;
for (int i = 1; i <= H; ++i)
for (int j = 1; j <= W; ++j)
{
cin >> a[i][j];
D[i][j] = INF;
}
deque<pii> dq;
D[1][1] = 0;
dq.emplace_back(1, 1);
while (!dq.empty())
{
auto u = dq.front();
int i = u.fi, j = u.sc;
dq.pop_front();
for (int k = 0; k < 4; ++k)
{
int x = i + dx[k], y = j + dy[k];
bool v = a[i][j] != a[x][y];
if (check(x, y) && D[x][y] > D[i][j] + v)
{
D[x][y] = D[i][j] + v;
if (v == 1) dq.emplace_back(x, y);
else dq.emplace_front(x, y);
}
}
}
int ans = 0;
for (int i = 1; i <= H; ++i)
for (int j = 1; j <= W; ++j)
if (D[i][j] != INF)
ans = max(ans, D[i][j]);
cout << ans + 1;
return 0;
}
