#include<iostream.h>
#include<stdio.h>
FILE *f=fopen("litere.in","r"),*g=fopen("litere.out","w");
int main()
{
	int n,i,j,op=0;
	char c[10001];
	int t=1;
	fscanf(f,"%d %s",&n,&c);
	while(t)
	{
		t=0;
		for(i=0;i<n-1;i++)
			if(c[i]>c[i+1])
			{
				char a;
				a=c[i];
				c[i]=c[i+1];
				c[i+1]=a;
				op++;
                                t=1;
			}
	}
	fprintf(g,"%d\n",op);
	return 0;
}