#include <bits/stdc++.h>
#define SKY
#define ll long long
#define ld long double
#define MASK(x) (1LL << x)
#define sz(x) (int)x.size()
#define ii pair<ll, ll>
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define pf push_front
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define set0(d) memset(d, 0, sizeof(d))
using namespace std;
const int LOG = 20;
const int base = 311;
const ll inf = 1e18;
const int block = 400;
const ll MOD = 1e9 + 7;
const int mxN = 1e6 + 66;
const int mxN2D = 4e3 + 55;
const int x[] = {0, 1, 0, -1};
const int y[] = {1, 0, -1, 0};
int H, W;
char grid[mxN2D][mxN2D];
bool safe(int x, int y)
{
return (x >= 0 && x < H && y >= 0 && y < W && grid[x][y] != '.');
}
void solve()
{
cin >> H >> W;
for (int r=0; r<H; r++)
{
for(int c=0; c<W; c++)
{
cin >> grid[r][c];
}
}
deque<ii> pq;
pq.push_back(mp(0, 0));
vector<vector<int>> depth(H, vector<int>(W, 0));
depth[0][0] = 1;
int ans = 1;
while(!pq.empty())
{
ii cell = pq.front();
pq.pop_front();
int u = cell.fi;
int v = cell.se;
ans = max(ans, depth[u][v]);
for (int i=0; i<4; i++)
{
int ux = u + x[i];
int vx = v + y[i];
if (safe(ux, vx) && !depth[ux][vx])
{
depth[ux][vx] = depth[u][v] + (grid[ux][vx] != grid[u][v]);
if (grid[ux][vx] == grid[u][v])
{
pq.push_front(mp(ux, vx));
} else
{
pq.push_back(mp(ux, vx));
}
}
}
}
cout << ans;
}
int main()
{
ios_base::sync_with_stdio(false);
#ifdef SKY
// freopen("test.inp", "r", stdin);
// freopen("test.out", "w", stdout);
#endif //SKY
solve();
return 0;
}
