This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define st first
#define nd second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define ll long long
ll mod=1000000007;
int inf=1000000007;
ll infl=1000000000000000007;
const int N=200007;
int r[N];
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n;
    string s;
    cin>>n>>s;
    s='#'+s;
    vector<int>Q0,Q1;
    for(int i=2*n;i>n;i--)
    {
        if(s[i]=='B') Q0.pb(i);
        else Q1.pb(i);
    }
    for(int i=1;i<=n;i++)
    {
        if(s[i]=='B')
        {
            r[i]=Q1.back();
            Q1.pop_back();
        }
        else
        {
            r[i]=Q0.back();
            Q0.pop_back();
        }
    }
    int ans=0;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<i;j++)
        {
            if(r[i]>r[j]) ans++;
        }
    }
    cout<<ans;
    return 0;
}
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