#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define pf push_front
#define sz(x) int(x.size())
#define all(x) x.begin(), x.end()
#define clz __builtin_clz
#define popcount __builtin_popcount
#define lb(x) lower_bound(x)
#define ub(x) upper_bound(x)
#define loop(i, j, n, k) for(int i = j; i <= n; i += k)
#define fast ios_base :: sync_with_stdio(0); cin.tie(0); cout.tie(0)
template <typename T>
inline void print(T x) { cerr << x << endl; }
template <typename T>
inline void print(vector <T> x) { cerr << '['; loop(i, 0, sz(x) - 2, 1) cerr << x[i] << ", "; cerr << x.back() << ']' << endl; }
template <typename T>
inline bool maximize(T &a, const T &b) { return a < b ? (a = b) : 0; }
template <typename T>
inline bool minimize(T &a, const T &b) { return a > b ? (a = b) : 0; }
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;
using pss = pair<string, string>;
using vll = vector<ll>;
using pll = pair<ll, ll>;
#define debug(x) cerr << #x << " = "; print(x)
mt19937 rng(chrono :: steady_clock :: now().time_since_epoch().count());
template <typename T>
inline int rand_range(T l, T r) { return uniform_int_distribution<T> (l, r)(rng); }
void setIO(string s) {
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
freopen("error.txt", "w", stderr);
}
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
int main() {
// setIO("task");
fast;
int n, m; cin >> n >> m;
vector<vi> matrix(n + 5, vi(m + 5, 0));
loop(i, 1, n, 1) {
loop(j, 1, m, 1) {
char c; cin >> c;
matrix[i][j] = (c == 'R' ? 1 : 2);
}
}
if(matrix[1][1] == 0) {
return cout << 0, 0;
}
auto valid = [&](int x, int y) -> bool {
return x <= n && y <= m && matrix[x][y] > 0;
};
vector<vi> dist(n + 5, vi(m + 5, 0));
deque<pii> dq;
dq.pb({1, 1});
dist[1][1] = 1;
int ans = 0;
while(sz(dq)) {
auto [x, y] = dq.front();
dq.pop_front();
ans = max(ans, dist[x][y]);
loop(i, 0, 3, 1) {
int nx = x + dx[i];
int ny = y + dy[i];
if(valid(nx, ny) && !dist[nx][ny]) {
if(matrix[nx][ny] == matrix[x][y]) {
dist[nx][ny] = dist[x][y];
dq.pf({nx, ny});
} else {
dist[nx][ny] = dist[x][y] + 1;
dq.pb({nx, ny});
}
}
}
}
cout << ans;
}
