Problem:
Score : 100 points

Problem Statement

Given is an integer N.

Takahashi chooses an integer a from the positive integers not greater than N with equal probability.

Find the probability that a is odd.

Constraints

1 \leq N \leq 100

Input

Input is given from Standard Input in the following format:

N

Output

Print the probability that a is odd.
Your output will be considered correct when its absolute or relative error from the judge's output is at most 10^{-6}.

Sample Input 1

4

Sample Output 1

0.5000000000

There are four positive integers not greater than 4: 1, 2, 3, and 4. Among them, we have two odd numbers: 1 and 3. Thus, the answer is \frac{2}{4} = 0.5.

Sample Input 2

5

Sample Output 2

0.6000000000

Sample Input 3

1

Sample Output 3

1.0000000000

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <stdio.h>
int main(void){
    long long a,b,t,x[100000],p=1,ans=0,i,j,k;
    scanf("%lld %lld", &a, &b);
    if(a>b)
    {
        t=b;
        b=a;
        a=t;
    }
    if(a==1)
    ans=1;
    x[0]=1;
    for(i=2; i<=a; i++)
    {
        if(a%i==0&&b%i==0)
        {
            x[p]=i;
            p++;
        }
    }
    for(i=1; i<p; i++)
    {
        a=1;
        for(j=i+1; j<p; j++)
        {
            for(k=2; k<x[i]; k++)
            {
                if(x[i]%k==0&&x[j]%k==0)
                {
                    a=0;
                    break;
                }
            }
            if(a<1)
            break;
        }
        ans+=a;
    }
    printf("%lld\n", ans);
    
    return 0;
}