/*
ID: Sho10
LANG: C++
TASK:
*/
#include <bits/stdc++.h> //JuniorMonster a.k.a Sho10
#define ll long long int
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#define all(a) (a).begin(), (a).end()
#define sz size
#define f first
#define s second
#define pb push_back
#define er erase
#define in insert
#define mp make_pair
#define pi pair
#define rc(s) return cout<<s,0
#define endl '\n'
#define mod 1000000007
#define PI 3.14159265359
#define CODE_START  ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
using namespace std;
ll n,ans=0;
string a,b;
int32_t main(){
CODE_START;
ifstream cin("litere.in");
ofstream cout("litere.out");
cin>>n;
cin>>a;
b=a;
sort(b.begin(),b.end());
for(ll i=0;i<n;i++)
{
    if(a[i]!=b[i]){
        for(ll j=i+1;j<n;j++)
        if(a[j]==b[i]){
            for(ll c=j;c>i;c--){
                swap(a[c],a[c-1]);
                ans++;
        }
        break;
    }
    }
}
cout<<ans<<endl;
}