#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int maxn = 4005;
int H, W;
char grid[maxn][maxn];
bool seen[maxn][maxn];
int dx[] = {0,1,0,-1};
int dy[] = {1,0,-1,0};
bool valid(int x, int y) {
return 0 <= x && x < H && 0 <= y && y < W;
}
bool cnt(pair<int,int>& p, char curr) {
for (int k = 0; k < 4; k++) {
int nx = p.first + dx[k];
int ny = p.first + dy[k];
if (!seen[nx][ny] && valid(nx,ny) && grid[nx][ny] == (curr=='R'?'F':'R')) return true;
}
return false;
}
int main()
{
ios_base::sync_with_stdio(false); cin.tie(NULL);
cin >> H >> W;
for (int i = 0; i < H; i++) {
for (int j = 0; j < W; j++) {
cin >> grid[i][j];
}
}
if (H == 1 && W == 1) {
cout << 1 << '\n';
return 0;
}
queue<pair<int,int>> q, nxt;
q.push({0,0});
seen[0][0] = true;
char curr = grid[0][0];
int ans = 0;
while (true) {
int added = 0;
//cout << "level " << ans << '\n';
//cout << q.size() << '\n';
while (!q.empty()) {
auto p = q.front(); q.pop();
nxt.push(p);
//cout << p.first << ' ' << p.second << '\n';
for (int k = 0; k < 4; k++) {
int nx = p.first + dx[k];
int ny = p.second + dy[k];
if (!valid(nx,ny)) continue;
if (seen[nx][ny]) continue;
if (grid[nx][ny] != curr) continue;
seen[nx][ny] = true;
q.push({nx,ny});
added++;
}
}
while (!nxt.empty()) {
auto p = nxt.front(); nxt.pop();
if (cnt(p,curr)) q.push(p);
}
/*
for (int i = 0; i < H; i++) {
for (int j = 0; j < W; j++) {
cout << seen[i][j];
}
cout << '\n';
}
*/
curr = curr == 'R' ? 'F' : 'R';
if (added == 0) break;
ans++;
}
cout << ans << '\n';
}
