UVA 11637 Garbage Remembering Exam

#include <iostream>
#include <stdio.h>
#include <cstring>
#include <math.h>
#define MAX 100010

using namespace std;
int n,k;
long double fac[MAX];

void GetFacs()
{
    for(int i=1;i<MAX;i++)
    {
        fac[i] = fac[i-1] + log((long double)i);
    }
}

double ExpectedValue()
{
    int x;
    double p,e = n;
    if(n==1) return 0;
    for(int i=1; i<=n; i++)
    {
        x = max(i-k-1,0) + max(n-i-k,0);
        if(x-2*k>=0)
        {
            p = fac[x]+fac[n-2*k-1]-fac[n-1]-fac[x-2*k];
            e -= exp(p);
        }
    }
    return e;
}

int main()
{
    int t=0;
    GetFacs();
    while(scanf("%d%d",&n,&k)!=EOF && !(n==0 && k==0))
    {
        printf("Case %d: %.4lf\n", ++t, ExpectedValue());
    }
    return 0;
}