#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#ifdef _WIN32
#define getchar_unlocked _getchar_nolock
#endif
//#define int long long
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define ppb pop_back
#define eb emplace_back
#define g0(a) get<0>(a)
#define g1(a) get<1>(a)
#define g2(a) get<2>(a)
#define g3(a) get<3>(a)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef double db;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef tuple<int, int, int> iii;
typedef tuple<int, int, int, int> iiii;
typedef tree<ii, null_type, less<ii>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
int H, W, ans, CNT, link[16000005], sz[16000005], dr[] = {-1, 0, 0, 1}, dc[] = {0, -1, 1, 0};
char tmp, F[4005][4005];
vector<int> vec[16000005];
inline int conv(int r, int c) {
return (r - 1) * W + c;
}
int find(int x) {
if (x == link[x]) return x;
return link[x] = find(link[x]);
}
void unite(int a, int b) {
a = find(a);
b = find(b);
if (a == b) return;
if (sz[b] > sz[a]) swap(a, b);
sz[a] += sz[b];
for (int j : vec[b]) vec[a].pb(j);
link[b] = a;
}
main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> H >> W;
for (int i = 1; i <= H; i++)
for (int j = 1; j <= W; j++) {
cin >> tmp;
if (tmp == '.') tmp = 2;
else if (tmp == 'R') tmp = 0;
else tmp = 1;
F[i][j] = tmp;
}
for (int i = 1; i <= H; i++)
for (int j = 1; j <= W; j++) {
if (F[i][j] == 2) continue;
CNT++;
link[conv(i, j)] = conv(i, j);
sz[conv(i, j)] = 1;
for (int k = 0; k < 4; k++)
if (1 <= i + dr[k] && i + dr[k] <= H && 1 <= j + dc[k] && j + dc[k] <= W && F[i + dr[k]][j + dc[k]] <= 1 && F[i + dr[k]][j + dc[k]] != F[i][j])
vec[conv(i, j)].eb(conv(i + dr[k], j + dc[k]));
}
for (int i = 1; i <= H; i++) {
for (int j = 1; j <= W; j++) {
if (F[i][j] == 2) continue;
for (int k = 0; k < 4; k++)
if (1 <= i + dr[k] && i + dr[k] <= H && 1 <= j + dc[k] && j + dc[k] <= W && F[i + dr[k]][j + dc[k]] <= 1 && F[i + dr[k]][j + dc[k]] == F[i][j])
unite(conv(i, j), conv(i + dr[k], j + dc[k]));
}
}
while (1) {
ans++;
if (sz[find(1)] == CNT) break;
vector<int> tmp;
for (int i : vec[find(1)]) tmp.pb(i);
for (int i : tmp) unite(1, i);
}
cout << ans << '\n';
}
