#include<stdio.h>
#define N 10001
int i,n,l,y[N],z[N][26];
char s[N],c;
int main()
{freopen("litera.in","r",stdin);
freopen("litera.out","w",stdout);
scanf("%d\n",&n);
for(i=1;i<=n;i++)
      scanf("%c",&s[i]),z[i][s[i]-'a']=++y[s[i]-'a'];
for(i=1;i<=n;i++)
for(c='a';c<='z';c++)
if(!z[i][c-'a'])
      z[i][c-'a']=z[i-1][c-'a'];
for(i=1;i<=n;i++)
for(c='a';c<s[i];c++)
      l+=z[n][c-'a']-z[i][c-'a'];
printf("%d",l);
return 0;}