1231

题目描述

There are n ants on a polygon. The polygon has n edges and every ant is on a corner at first. Than the ants start to move on edges. A corner connects two edges, so the ants choose to move on one edge of the two randomly. If two ants move on a same edge , they will be angry. Give you the number n. Calculate the probability that there exists some ants angry, after their first choice.

输入

Multiple cases. Every case takes a line with the number n. (3 <= n <= 15)

输出

A case a line.Print the probability, with exactly 6 digits after the decimal point. 

样例输入

4

样例输出

0.875000

提示

#include<stdio.h>#include<math.h>int main(){    int n,i;    while(scanf("%d",&n)!=EOF)    printf("%.6f\n",1-pow(0.5,n-1));    return 0;}