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 sosu(int n){
  int i;

  /* 自然数 */

  /* 判定フラグ */
  int flag = 0;

  /* 自然数の入力 */

  /* 素数かどうかを判定 */
  for( i=2;i<n;++i ) {
    if( n%i==0 ) {
      flag = 1;
      break;
    }
  }

  /* 判定結果を出力 */
  if( flag==0 ){//素数
    return 1;
  }else{
    return -1;
 }
  return 0;
}



int main(){
  int a,b;
  scanf("%d %d",&a,&b);
  int sum=1;
  int i,k;
  for(i=2;i<=a&&i<=b;i++){
    k=sosu(i);
    if(k==1){
      if(a%i==0&&b%i==0){
        sum++;
      }
    }
  }
  printf("%d",sum);
  return 0;
}