#include<stdio.h>
using namespace std;
#define dim 10001
long a[dim];
char s;
int main()
{FILE *f=fopen("litere.in","r"), *g=fopen("litere.out","w");
int i,n,schimb=0,j,sss=0;
	fscanf(f,"%ld ",&n);
	
for(i=1;i<=n;i++)
	{fscanf(f,"%c",&s);
	a[++sss]=(int)s-96;
	}
	
for(i=2;i<=n;i++)
	for(j=i;j>=1;j--)
		if(a[j]>a[i])
			schimb++;
fprintf(g,"%ld\n",schimb);
	

fclose(f);
fclose(g);

return 0;}