#include<stdio.h>
#include<string.h>
int n,i,gata,aux;
char huge v[10001];
long long nr;
int main ()
{
freopen("litere.in", "r", stdin);
freopen("litere.out", "w", stdout);
scanf("%d%c", &n,&v[0]);
for(i=1;i<=n;i++)
   scanf("%c", &v[i]);
gata=1;
while(gata)
{
gata=0;
 for(i=1;i<=n-1;i++)
   if(v[i]>v[i+1])
	  {
	   aux=v[i];
	   v[i]=v[i+1];
		 v[i+1]=aux;
	   gata=1;
	   nr++;
	  }
}
printf("%lld", nr);
return 0;
}