SGU 495. Kids and Prizes 期望

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <math.h>
using namespace std;
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        double p=(double)(n-1)/n;
        double ans=n-n*pow(p,m);
        printf("%.10lf\n", ans);
    }
    return 0;
}