//#include<iostream.h>
//#include<conio.h>
#include<fstream.h>

using namespace std;

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

int main()
{
char c[10000];
int i=0,j;
int sc=0,N;
f>>N;
while(!f.eof())f>>c[++i];

for(i=1;i<N;i++)
for(j=i+1;j<=N;j++)
if(c[j]<c[i])sc++;
 if(c[j]==c[i]){sc=sc+(N-j); c[j]=c[j++];}

//cout<<"sc : "<<sc;
g<<sc;

//getch();
return 0;
}