#include<fstream>
#include<iostream>
using namespace std;
ifstream f("litere.in");
ofstream g("litere.out");
int main()
{
    unsigned int n,i,j,k=0,ind=1,x;
    char s[10001];
    f>>n;
    for(i=0;i<n;i++)
        f>>s[i];
    for(j=n-1;j>0 && ind;j--)
    {
        ind=0;
        for(i=0;i<j;i++)
        if(s[i]>s[i+1])
        {
            x=s[i];
            s[i]=s[i+1];
            s[i+1]=x;
            ind=1;
            k++;
        }
    }
    g<<k;
return 0;
}