/*
 * n 種のガチャポンなり食玩なりを
 * m 回でコンプリートする確率
 * <URL:http://aquarius10.cse.kyutech.ac.jp/~otabe/shokugan/>
 */

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

static int verbose;

/*
 * nCr  = n! / r! / (n - r)!
 */
static long long
combination(int n, int r)
{
	int i;
	long long x = 1;
	long long y = 1;
	for (i = 0; i < r; i++) {
		x *= n--;
		y *= (i + 1);
	}
	return x / y;
}/* combination */

static double
ipow(double x, int n)
{
	int i;
	double y = 1.0;
	for (i = 0; i < n; i++) {
		y *= x;
	}
	return y;
}/* ipow */

static double
nn_p(int ntypes, int times)
{
	int i;
	double sign = (ntypes % 2 == 0) ? -1 : 1;
	double sigma = 0;
	for (i = 0; i < ntypes; i++) {
		sigma += sign * combination(ntypes - 1, i) * ipow((double)(i + 1) / ntypes, times - 1);
		sign = sign < 0 ? 1 : -1;
	}
	return sigma;
}/* nn_p */

int
main(int argc, char *argv[])
{
	int ex = 1, ch, show_usage = 0;
	while ((ch = getopt(argc, argv, "vV")) != EOF) {
		switch (ch) {
		default:
		case 'V':
			show_usage++;
			break;
		case 'v':
			verbose++;
			break;
		}/* switch */
	}/* while */
	if (argc - optind != 2 || show_usage) {
		fprintf(stderr, "usage: %s [-v] n m\nCalculate probability of complete n types by m times.\n", argv[0]);
	}
	else {
		int ntypes = strtol(argv[optind], NULL, 0);
		int times = strtol(argv[optind + 1], NULL, 0);
		printf("%d %d = %.13g\n", ntypes, times, nn_p(ntypes, times));
		ex = 0;
	}
	return ex;
}/* main */