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>

long gcd(long x, long y) {
	if (y == 0) return x;
	return gcd(y, x%y);
}

int main() {
	long A, B, G_Common, k, cnt, i, j;
	scanf("%ld %ld",&A,&B);
	G_Common = gcd(A,B);
	/*while ((k = A%B) > 0) {
		A = B;
		B = k;
	}*/

	G_Common = B;
	cnt = 1;
	for (i = 2; G_Common > 1 && G_Common >= i*i; ) {
		for (j = 0; G_Common % i == 0; j++) G_Common /= i;
		if (j > 0) cnt++;
		if (i == 2) i++;
		else i += 2;
	}
	if (G_Common >= i) cnt++; //残りの素因数が2乗より小さい時
	printf("%ld\n",cnt);
	return 0;
}