#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif
/*
*/
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
void solve(int test_case)
{
ll n; cin >> n;
string s; cin >> s;
s = "$" + s;
vector<ll> pos1,pos2;
rep1(i,2*n){
if(s[i] == 'B') pos1.pb(i);
else pos2.pb(i);
}
ll ans = 0;
rep(i,n){
vector<pll> segs;
for(int j = i, iter = 0; iter < n; j = (j+1)%n, iter++){
ll l = pos1[iter], r = pos2[j];
if(l > r) swap(l,r);
segs.pb({l,r});
}
ll cnt = 0;
rep(x,n){
for(int y = x+1; y < n; ++y){
auto [l1,r1] = segs[x];
auto [l2,r2] = segs[y];
if(l1 > l2) swap(l1,l2), swap(r1,r2);
if(l1 < l2 and l2 < r1 and r1 < r2){
cnt++;
}
}
}
amax(ans,cnt);
}
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
