1 #include<iostream>
 2 #include<cstdio>
 3 
 4 using namespace std;
 5 
 6 double f[2501][2501];
 7 int n;
 8 
 9 int main() {
10     scanf("%d",&n);
11     n /= 2;
12     for(int i = 2;i <= n; i++)
13         f[i][0] = f[0][i] = 1;
14     for(int i = 1;i <= n; i++)
15         for(int j = 1;j <= n; j++)
16             f[i][j] = (f[i-1][j] + f[i][j-1]) * 0.5;
17     printf("%.4lf",f[n][n]);
18     return 0;
19 }