///KhoaHo///
#include<bits/stdc++.h>
using namespace std;
///define-zone
#define task "test"
#define vec vector
#define priq priority_queue
#define pf push_front
#define pb push_back
#define popb pop_back
#define popf pop_front
#define SZ(a) a.begin(), a.end()
#define SZZ(a, begin, end) a + begin, a + begin + end
#define fi first
#define se second
#define BIT(n) (1 << n)
///typedef-zone
typedef long long ll;
typedef unsigned long long ull;
typedef long double ldb;
typedef double db;
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
///code-mau
template<class val> inline val gcd(val a, val b){ return (a ? gcd(b%a, a): b);}
template<class val> inline val fmul(val a, val b, val m){ if (!b) return 0; if (!(b-1)) return a; if (b%2) return (fmul(a, b/2, m)*2+a)%m; else return (fmul(a, b/2, m)*2)%m; }
template<class val> inline bool getbit(val pos, val mask) {return ((mask >> pos)&1);}
void fastio()
{
ios_base::sync_with_stdio(NULL);
cin.tie(NULL);
cout.tie(NULL);
}
void init()
{
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
const int N = 4004;
string snows[N];
int n, depth[N][N], ans = 1, m;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, -1, 0, 1};
bool check(int x, int y)
{
return ((x >= 0)&&(x < n)&&(y < m)&&(y >= 0)&&(snows[x][y] != '.'));
}
int main()
{
fastio();
///init();
cin >> n >> m;
for(int i = 0; i < n; i++) cin >> snows[i];
deque<ii> dq;
depth[0][0] = 1;
dq.pb(ii(0, 0));
while(!dq.empty())
{
int x = dq.front().fi;
int y = dq.front().se;
dq.popf();
ans = max(ans, depth[x][y]);
for(int i = 0; i < 4; i++)
{
int xx = x + dx[i];
int yy = y + dy[i];
if((check(xx, yy))&&(!depth[xx][yy]))
{
if(snows[x][y] == snows[xx][yy])
{
depth[xx][yy] = depth[x][y];
dq.pf(ii(xx, yy));
} else
{
depth[xx][yy] = depth[x][y] + 1;
dq.pb(ii(xx, yy));
}
}
}
}
cout << ans;
return 0;
}
