#include <bits/stdc++.h>

using namespace std;

ifstream in("litere.in");
ofstream out("litere.out");

int main()
{
    int n,i,k=0,sw;
    char x,v[10000];
    in>>n;
    in>>v;
    do
    {
        sw=1;
        for(i=0;i<n-1;i++)
            if(v[i]>v[i+1])
                swap(v[i],v[i+1]),sw=0,k++;

    }while(sw==0);
    out<<k;
    return 0;
}