#include <bits/stdc++.h>
using namespace std;
#define dbgv(v) cout<<#v<<" = "; f(i,0,v.size()) cout<<v[i]<<" "; cout<<endl
#define dbga(a,x,y) cout<<#a<<" = "; f(i,x,y) cout<<a[i]<<" "; cout<<endl
#define erorp(x) cout<<#x<<"={"<<(x.F)<<" , "<<x.S<<"}"<<endl
#define eror(x) cout<<#x<<'='<<(x)<<endl
#define f_(i,a,b) for(int i=a;i>=b;i--)
#define f(i,a,b) for(int i=a;i<b;i++)
#define nb(x) __builtin_popcount(x)
#define all(v) v.begin(),v.end()
#define bit(n,k) (((n)>>(k))&1)
#define Add(x,y) x=(x+y)%mod
#define maxm(a,b) a=max(a,b)
#define minm(a,b) a=min(a,b)
#define lst(x) x[x.size()-1]
#define sz(x) int(x.size())
#define mp make_pair
#define ll long long
#define pb push_back
#define S second
#define F first
#define int ll
const int N=1e6+99;
int n,t,a[N];
ll ans;
string s;
vector<int> vec0,vec1;
bool check(int lx,int rx,int ly,int ry){
if(lx>rx) swap(lx,rx);
if(ly>ry) swap(ly,ry);
if(lx>ly) swap(lx,ly),swap(rx,ry);
return ly<rx && rx<ry;
}
int32_t main(){
ios:: sync_with_stdio(0), cin.tie(0), cout.tie(0);
cin>>n>>s;
f(i,0,n<<1){
if(s[i]=='B') vec0.pb(i);
else vec1.pb(i);
}
f(shift,0,n){
//if(shift!=1) continue ;
ll res=0;
f(i,0,n){
f(j,i+1,n){
res+=check(vec0[i],vec1[(i+shift)%n],vec0[j],vec1[(j+shift)%n]);
//cout<<i<<" "<<j<<" -> "<<check(vec0[i],vec1[(i+shift)%n],vec0[j],vec1[(j+shift)%n])<<endl;
}
}
maxm(ans,res);
}
cout<<ans;
}
