#include <stdio.h>
int main()
{
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	int n,i,r=0,j,s=0,sch,t;
	char v[10005],x;
	scanf("%d",&n);
	while (scanf("%c",&x) != EOF)
		v[++r]=x;
	do
	{
		sch=0;
		for (i=2; i<=n; i++)
			if (v[i]>v[i+1])
			{
				t=v[i];
				v[i]=v[i+1];
				v[i+1]=t;
				sch=1;
				s++;
			}
	}
	while(sch);
	printf("%d",s);
	return 0;
}