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>
#include <math.h>


int isprime(int x){
    for(int i = 2; i <= sqrt(x); i++){
        if (x % i == 0)
            return 0;
    }
    return 1;
}
int main(){
    int a,b,t = 0;

    scanf("%d%d", &a, &b);

    for(int i = 1; i <= a && i <= b; i ++){
        if(a % i == 0 && b % i == 0){
            if(isprime(i)){
                t++;
            }
        }
    }
    printf("%d",t);

    return 0;
}