#include <bits/stdc++.h>
#define fi first
#define se second
using namespace std;
using ll = long long;
const int maxN = 4e3 + 1;
const int MOD = 1e9 + 7;
struct TCell
{
int x, y;
};
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
int n, m, deg[maxN][maxN];
char a[maxN][maxN];
void ReadInput()
{
cin >> n >> m;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++)
cin >> a[i][j];
}
bool IsOut(const TCell &u)
{
return u.x < 1 || u.x > n || u.y < 1 || u.y > m;
}
void Solve()
{
int res = 1;
deg[1][1] = 1;
deque<TCell> Q;
Q.push_front({1, 1});
while (!Q.empty())
{
TCell u = Q.front();
Q.pop_front();
res = max(res, deg[u.x][u.y]);
for (int i = 0; i < 4; i++)
{
TCell v = {u.x + dx[i], u.y + dy[i]};
if (!IsOut(v) && a[v.x][v.y] != '.')
{
a[v.x][v.y] = '.';
if (a[v.x][v.y] == a[u.x][u.y])
{
deg[v.x][v.y] = deg[u.x][u.y];
Q.push_front(v);
}
else
{
deg[v.x][v.y] = deg[u.x][u.y] + 1;
Q.push_back(v);
}
}
}
}
cout << res;
}
#define task ""
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
//freopen(task".INP", "r", stdin);
//freopen(task".OUT", "w", stdout);
int T = 1;
//cin >> T;
while (T--)
{
ReadInput();
Solve();
}
}
