#include<stdio.h>
using namespace std;
#define dim 10001
int a[dim];
char s;
int main()
{FILE *f=fopen("litere.in","r"), *g=fopen("litere.out","w");
int i,n,m,ss=0,sss=0,schimb=0,j,k;
	fscanf(f,"%d ",&n);
	m=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,"%d\n",schimb);
	

fclose(f);
fclose(g);

return 0;}