#include<stdio.h>
long nr;
int n;
char s[10001];


void read()
{
scanf("%d\n",&n);
scanf("%s",s);
}

void bub()
{
int r;
int i;
char aux;
do
{
r=1;
for (i=0;i<n-1;i++)
   {
    if (s[i]>s[i+1])
      {r=0;
      nr++;
      aux=s[i];
      s[i]=s[i+1];
      s[i+1]=aux;
      }
   }
}
while (!r);
}

int main()
{
freopen("litere.in","r",stdin);
freopen("litere.out","w",stdout);
read();
bub();
printf("%ld",nr);
fcloseall();
return 0;
}