#include <stdio.h>
double sum (int k, double x)
{
    int i, j;
    double s, o, h;
        s = 0;
        j = -1;
        o = x;
    for (i=1; i<=k;i++)
    {h= (j*o) / i;
        s += (j*o) / i;
        j = -j;
        o *= x;
    }
    return(s);
}
int main(void)
{
    int n;
    double h, res;
    scanf_s("%d", &n);
    scanf_s("%lf", &h);
    res = sum(n, h);
    printf("%f", res);
    return(0);
}