#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
//#define int long long
namespace gtx{
//	Fast IO
	void read(int &x){
		x = 0;int h = 1;char tmp;
		do{tmp=getchar();if(tmp=='-')h*=-1;}while(!isdigit(tmp));
		while(isdigit(tmp)) x*=10,x+=tmp-'0',tmp=getchar();
		x*=h;
	}
	void read(char &x){do{x=getchar();}while(x==' '||x=='\n'||x=='\r');}
	void write(char x){putchar(x);}
	void write(int x){
		if(x<0) putchar('-'),x=-x;int st[200]={0},tot=0;
		do st[++tot]=x%10,x/=10; while(x);
		while(tot){putchar(st[tot--]+'0');}
	}
	void write(int x,char y){write(x);write(y);}
	#ifndef int
	void read(long long &x){
		x = 0;int h = 1;char tmp;
		do{tmp=getchar();if(tmp=='-')h*=-1;}while(!isdigit(tmp));
		while(isdigit(tmp)) x*=10,x+=tmp-'0',tmp=getchar();
		x*=h;
	}
	void write(long long x){
		if(x<0) putchar('-'),x=-x;int st[200]={0},tot=0;
		do st[++tot]=x%10,x/=10; while(x);
		while(tot){putchar(st[tot--]+'0');}
	}
	void write(long long x,char y){write(x);write(y);}
	#endif
	const int MAXN = 120;
	int n,ans;
	char a[MAXN];
	void check(){
		vector<pair<char,int>> v;
		for(int i = 1;i<=n;i++){
			int j = i;
			int cnt = 0;
			while(a[j]==a[i]&&j<=n){
				cnt++;j++;
			}
			v.push_back({a[i],cnt});
			i = j-1;
		}
		int now = 0;
		for(int i = 1;i<v.size()-1;i++){
			if(v[i].first=='W'){
				if(v[i-1].first=='B'&&v[i+1].first=='B') return;
			}else if(v[i].first=='B'){
				if(v[i-1].first=='W'&&v[i+1].first=='W') now+=v[i].second;
			}
		}
		ans = max(ans,now);
	}
	signed main(){
		scanf("%d%s",&n,a+1);
		for(int i = 1;i<=n;i++){
			if(a[i]=='.'){
				a[i] = 'W';
				check();
				a[i] = '.';
			}
		}
		write(ans);
		return 0;
	}
}
signed main(){
//	freopen("capture.in","r",stdin);
//	freopen("capture.out","w",stdout);
//	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	int T = 1;
//	gtx::read(T);
	while(T--) gtx::main();
	return 0;
}