#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main()
{
	freopen("litere.in","r",stdin);
	freopen("litere.out","w",stdout);
	
	int n, i, j, sort = 0;
	long contor = 0;
	char s[10003], aux;
	scanf("%d",&n);
	scanf("%s",&s);

	for (i = sort; i < n - 1; i++)
	{
		if (s[i] > s[i + 1])
		{
			aux = s[i];
			s[i] = s[i + 1];
			s[i + 1] = aux;
			contor++;
		}
		for (j = i; j > sort; j--)
			if (s[j] < s[j - 1])
			{
				aux = s[j];
				s[j] = s[j - 1];
				s[j - 1] = aux;
				contor++;
			}
			else break;
	}

	printf("%ld\n",contor);
	return 0;
}