#include <bits/stdc++.h>
using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
int n,nr=0,v[10001],k=0,x,MIN=100000,c;
char a;
int main()
{
    in>>n;
    while(n)
        in>>a,v[++k]=(int)a,n--;
    for(int i=1;i<k;i++)
        for(int j=1;j<=k-i;j++)
        if(v[j]>v[j+1])
          swap(v[j],v[j+1]),nr++;
    out<<nr;

    return 0;
}
///1 2 1 3 3 2 1 1 3
///1 1 2 1 2 2 3 4 3