#include <stdio.h>
#include <string.h>
FILE *in,*o;
char s[100],a;
int i,n,f,nr=0;
main()
{
in=fopen("litere.in","r");
o=fopen("litere.out","w");
fscanf(in,"%d",&n);
for (i=1;i<=n;i++)
fscanf(in,"%c",&s[i]);
f=0;
while (f==0)
{
f=1;
for(i=1;i<n;i++)
if (s[i]>s[i+1])
		{
		a=s[i];
		s[i]=s[i+1];
		s[i+1]=a;
		nr++;
		f=0;
		}
}
fprintf(o,"%d",nr);
fclose(in);
fclose(o);
return 0;
}