//雪花飄飄北風嘯嘯
//天地一片蒼茫
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
#define int long long
#define ll long long
#define ii pair<ll,ll>
#define iii pair<ii,ll>
#define fi first
#define se second
#define endl '\n'
#define debug(x) cout << #x << " is " << x << endl
#define rep(x,start,end) for(auto x=(start)-((start)>(end));x!=(end)-((start)>(end));((start)<(end)?x++:x--))
#define all(x) (x).begin(),(x).end()
#define sz(x) (int)(x).size()
#define indexed_set tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>
//change less to less_equal for non distinct pbds, but erase will bug
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
int fen[400005];
void upd(int i){
while (i<400005){
fen[i]++;
i+=i&-i;
}
}
int query(int i){
int res=0;
while (i){
res+=fen[i];
i-=i&-i;
}
return res;
}
int query(int i,int j){
return query(j)-query(i);
}
ii mp(int i,int j){
if (i<j) return ii(i,j);
else return ii(j,i);
}
int n;
string s;
vector<int> b,w;
int eval(int x){
memset(fen,0,sizeof(fen));
vector<ii> edge;
rep(y,0,n) edge.push_back(mp(b[y],w[(x+y)%n]));
sort(all(edge));
ll curr=0;
for (auto &it:edge){
curr+=query(it.fi,it.se);
upd(it.se);
}
return curr;
}
int solve(int l,int r){
int m1,m2;
while (r-l>3){
m1=(r+l)>>1;
m2=m1+1;
if (eval(m1)>eval(m2)) r=m1;
else l=m2;
}
int ans=0;
rep(x,l,r+1) ans=max(ans,eval(x));
return ans;
}
main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin.exceptions(ios::badbit | ios::failbit);
cin>>n;
cin>>s;
rep(x,0,2*n){ //so im gonna 1 index because fenwick
if (s[x]=='B') b.push_back(x+1);
else w.push_back(x+1);
}
if (n==1) cout<<0<<endl;
else{
int ans=0;
int curr=0;
int inc=max(n/2+5,1LL);
while (curr<n){
ans=max(ans,solve(curr,min(curr+inc-1,n-1)));
curr+=inc;
}
cout<<ans<<endl;
}
}
