#include <stdio.h>            
int n;
char v[10000];            
int main()   
{freopen("litere.in","r",stdin);   
scanf("%d\n",&n);
gets(v);   
int nr=0;
for (int i=0;i<n;++i)
{   
char v1=v[i];   
int j;   
for (j=i-1;j>=0;--j)   
{   
if (v[j]<=v1) break;   
v[j+1]=v[j];   
nr++;   
}   
v[j+1]=v1;   
}   
freopen("litere.out","w",stdout);   
printf("%d",nr);   
return 0;}