#include <bits/stdc++.h>
using namespace std;
#define fastIO ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL)
#define PI acos(-1.0)
#define FF first
#define SS second
#define eps 1e-9
// vector
#define pb push_back
#define sz(v) int((v).size())
#define all(v) (v).begin(), (v).end()
#define lb lower_bound
#define ub upper_bound
// bit
#define CNTBIT(x) __builtin_popcount(x)
#define ODDBIT(x) __builtin_parity(x)
#define MASK(i) (1ll<<(i))
#define BIT(x, i) (((x)>>(i))&1)
#define SUBSET(big, small) (((big)&(small))==(small))
#define MINBIT(x) (x)&(-x)
// typedef
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> ii;
typedef pair<int, ii> i3;
/* CODE BELOW */
const int N=1e3+7, M=18;
const int MOD=1e9+7;
const int oo=1e9+9;
int n, m, k, t;
int tr[4]{-1, 0, 0, 1};
int tc[4]{0, -1, 1, 0};
int a[N][N];
bool mark[N][N];
int get(char c) {
if(c=='T') return 1;
if(c=='B') return 2;
return 0;
}
bool check(int x, int y) {
return (x>0&&y>0&&x<=n&&y<=m&&a[x][y]);
}
int bfs(int si, int sj) {
queue<ii> q, nxtq;
q.push(ii(si, sj));
int ui, uj, vi, vj, cnt=0;
do{
cnt++;
while(sz(q)) {
tie(ui, uj)=q.front(), q.pop();
for(int i=0;i<4;i++) {
vi=ui+tr[i], vj=uj+tc[i];
if(!check(vi, vj)||mark[vi][vj]) continue;
mark[vi][vj]=1;
if(a[ui][uj]==a[vi][vj]) q.push(ii(vi, vj));
else nxtq.push(ii(vi, vj));
}
}
while(sz(nxtq)) q.push(nxtq.front()), nxtq.pop();
}while(sz(q));
return cnt;
}
signed main() {
//freopen("test.inp", "r", stdin);
//freopen("test.out", "w", stdout);
//fastIO;
scanf("%d%d\n", &n, &m);
char ch[m+1];
for(int i=1;i<=n;i++) {
scanf("%s\n", &ch);
for(int j=1;j<=m;j++) {
a[i][j]=get(ch[j-1]);
}
}
printf("%d", bfs(n, m));
return 0;
}
/* stuff you should look for
- int overflow, array bounds
- special/edge cases (n=1?)
- do smth instead of nothing and stay organized
- WRITE STUFF DOWN
- DONT JUST STICK ON ONE APPROACH
*/
