#include <bits/stdc++.h>
// #pragma GCC optimize(2)
#define int long long
#define pii pair<int, int>
#define tpi tuple<int, int, int, int>
#define il inline
#define p_q priority_queue
#define u_m unordered_map
#define bt bitset
#define rg register

using namespace std;

const int N1 = 300005;
const int N2 = 1000006;
const int mod = 998244353;

using i64 = long long;

void chmin(int& x, int c) {
	x = min(x, c);
}
void chmax(int& x, int c) {
	x = max(x, c);
}

#define debug 1
// #define multi_test_ 1
#define endl '\n'

int _test_ = 1;

namespace zqh {
	int n;
	string s;

	bool check_white() {
		for (int i = 1; i <= n; i++) {
			if (s[i] != 'B') continue;
			bool flag = false;
			int l = 0;
			for (int j = i + 1; j <= n; j++) {
				if (s[j] == '.') {
					flag = false;
					break;
				}
				if (s[j] == 'B') {
					flag = true;
					break;
				}
				l++;
			}
			if (flag && l > 0) return true;
		}
		return false;
	}
	int check_black() {
		for (int i = 1; i <= n; i++) {
			if (s[i] != 'W') continue;
			bool flag = false;
			int l = 0;
			for (int j = i + 1; j <= n; j++) {
				if (s[j] == '.') {
					flag = false;
					break;
				}
				if (s[j] == 'W') {
					flag = true;
					break;
				}
				l++;
			}
			if (flag && l) return l;
		}
		return 0;
	}

	void init() {
		cin >> n >> s;
		n = s.size();
		s = " " + s;
	}

	void solve() {
		int ans = 0;
		for (int i = 1; i <= n; i++) {
			if (s[i] != '.') continue;
			s[i] = 'W';
			if (!check_white()) {
				int t = check_black();
				ans = max(ans, t);
			}
			s[i] = '.';
		}
		cout << ans;
	}

	void main() {
		init();
		solve();
	}
}  // namespace zqh

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
#ifdef debug
#endif
#ifdef multi_test_
	cin >> _test_;
#endif
	while (_test_--) {
		zqh::main();
	}
	return 0;
}
/*

*/