#include <bits/stdc++.h>

using namespace std;
ifstream in("litere.in");
ofstream out("litere.out");
int n,nr,i,j;
char x[10001];
int main()
{
    in>>n,in.ignore(),in.getline(x,10000);
    bool ok=1;
   while(ok)
   {
       ok=0;
       for(i=0;i<strlen(x)-1;++i)
            if(x[i]>x[i+1])
            swap(x[i],x[i+1]),ok=1,nr++;
   }
    out<<nr;
    return 0;
}