#include<bits/stdc++.h>
#define st first
#define nd second
#define mp make_pair
#define pb push_back
#ifndef LOCAL
#define cerr if(0)cerr
#endif
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using vi = vector<int>;
int n;
void inc(int& x) {
x = (x+1)%(2*n);
}
string s;
ll solve(int i) {
ll ans = 0;
vector<bool> intersect(2*n, 1);
int cnt = 1;
vector<int> matched(2*n, -1);
matched[0] = matched[i] = 0;
int b = 1, w = i;
inc(w);
int iter = 1;
while(iter<n) {
while(s[b]!=s[0]) {
if(matched[b] != -1) {
intersect[matched[b]] = !intersect[matched[b]];
if(intersect[matched[b]]) {
cnt++;
}
else {
cnt--;
}
}
inc(b);
}
while(s[w]==s[0]) {
if(matched[w] != -1) {
intersect[w] = !intersect[w];
if(intersect[w]) {
cnt++;
}
else {
cnt--;
}
}
inc(w);
}
matched[b] = matched[w] = b;
ans += cnt;
cnt++;
iter++;
inc(b); inc(w);
}
return ans;
}
int main() {
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>n;
cin>>s;
ll best = 0;
vector<int> pos;
for(int i=1; i<2*n; ++i) {
if(s[i] != s[0]) pos.push_back(i);
}
int lo = 0, hi = pos.size()-1;
while(lo<=hi) {
int range = (hi-lo)/3;
ll f1 = solve(pos[lo + range]);
ll f2 = solve(pos[hi - range]);
best = max({best, f1, f2});
if(f1 <= f2) {
lo = lo + range + 1;
}
else {
hi = hi - range - 1;
}
}
cout<<best;
}
