#include <bits/stdc++.h>
using namespace std;
typedef long long ll;;
typedef pair<int, int> pii;
#define FOR(i, j, n) for(int i = j; i<= n; i++)
#define ROF(i, n, j) for(int i = n; i>= j; i--)
#define pb push_back
#define S second
#define F first
#define IOS ios_base :: sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define G(i, j) get<j-1>(i)
#define print(i) cout << #i << ": " << i
#define mp make_pair
const int mn = 2000 + 10;
int a[2*mn];
int g1[mn], g2[mn], p[mn];
pii s[mn*2];
struct Seg_tree
{
struct Node
{
int ted = 0;
}node[mn*4];
void init(int id, int L, int R)
{
node[id].ted = 0;
if (L+1 == R) return;
int mid = (L+R)/2;
init(id*2, L, mid);
init(id*2 + 1, mid, R);
}
void update(int id, int L, int R, int ind)
{
node[id].ted++;
if (L+1 == R) return;
int mid = (L+R)/2;
if (ind >= mid) update(id*2 + 1, mid, R, ind);
else update(id*2, L, mid, ind);
}
int get(int id, int L, int R, int l, int r)
{
if (L == l and R == r) return node[id].ted;
int mid = (L+R)/2;
if (l >= mid) return get(id*2 + 1, mid, R, l, r);
else if (r <= mid) return get(id*2, L, mid, l, r);
else return get(id*2, L, mid, l, mid) + get(id*2 + 1, mid, R, mid, r);
}
}seg[mn];
signed main()
{
IOS;
int n;
cin >> n;
string s2;
cin >> s2;
int tmp1 = 0, tmp2 = 0;
FOR(i, 0, 2*n-1)
{
if (s2[i] == 'B')
{
g1[tmp1] = i;
a[i] = 1;
tmp1++;
}
else
{
g2[tmp2] = i;
a[i] = 2;
tmp2++;
}
}
int out = 0;
FOR(d, 0, n-1)
{
int ans = 0;
FOR(i, 0, n-1)
{
s[i] = mp(min(g1[i], g2[(i+d)%n]), max(g1[i], g2[(i+d)%n]));
}
sort(s, s+n);
FOR(i, 0, n-1)
{
ans += seg[d].get(1, 1, 2*n+1, s[i].F+1, s[i].S+1);
seg[d].update(1, 1, 2*n+1, s[i].S+1);
}
out = max(out, ans);
}
cout << out;
return 0;
}
