#include<stdio.h>

#define N 10001

int n;

char v[N];

void citire()
{
	scanf("%d",&n);
	scanf("%s",v);
}

void calcul()
{
	int i,ax,cn=n,rez=0;
	bool ok=0;
	while (ok==0)
		for( i=0 , ok=1 , --cn ; i<=cn-1 ; ++i )
			if(v[i]>v[i+1])
			{
				ax=v[i];
				v[i]=v[i+1];
				v[i+1]=ax;
				ok=0;
				++rez;
			}
	printf("%d",rez);
}

int main()
{
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	citire();
	calcul();
	return 0;
}