#include <stdio.h>

char sir[10001], aux;
int n, i, j, k;
int mutari = 0, poz;


int maxim (int p2)
{
	int pozitie = 0, z;
	char Max = 'a';
	for (z=0; z<=p2; ++z)
		if (Max <= sir[z])
		{
			Max = sir[z];
			pozitie = z;
		}
	return pozitie;
}

int main()
{
	FILE *f = fopen ("litere.in","r");
	FILE *g = fopen ("litere.out","w");
	fscanf (f,"%d", &n);
	fscanf (f,"%s", sir);
	fclose(f);
	
	do
	{
		n --;
		poz = maxim (n);
		//printf ("%2d : ", poz);
		
		for (i=poz; i<n; ++i)
		{
			aux = sir[i];
			sir[i] = sir[i+1];
			sir[i+1] = aux;
			mutari ++;
		}
		
		//printf ("%s\n", sir);
	}
	while (n > 0);
	
	//printf ("mutari = %d", mutari);
	
	fprintf (g,"%d", mutari);
	fclose(g);
	
	return 0;
}