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

#define MAXN 10005

int N;
char x[MAXN], newx[MAXN];

int main()
{
	freopen("litere.in", "rt", stdin);
	freopen("litere.out", "wt", stdout);

	scanf("%d", &N);
	for (int i = 0; i < N; i++)
		scanf(" %c", x + i);

	int NR = 0;
	for (char c = 'z'; c >= 'a'; c--)
	{
		memset( newx, 0, sizeof(newx) );
		for (int i = 0, j = 0; x[i]; i++)
		{
			if (x[i] >= c)
				continue;

			NR += i - j;
			newx[j++] = x[i];
		}
		memcpy( x, newx, sizeof(x) );
	}

	printf("%d\n", NR);
	return 0;
}