#include <stdio.h>
#include <math.h>

double f(double x, double p, int n, int k) { return (n == k) ? 0 : p / k - f(x, p * x, n, k + 1); }

int main() {
  int n;
  double x;
  do {
    do { printf("n = "); } while (scanf("%d", &n) != 1);
    do { printf("x = "); } while (scanf("%lf", &x) != 1);
  } while (!(fabs(x) < 1.0 && n > 0));
  printf("%f\n", f(x, x, n, 1));
  return 0;
}
/* end */