#include<bits/stdc++.h>
using namespace std;
const int N=1255;
double f[N][N][2];
int n;
int main(){
	scanf("%d",&n),n>>=1;
	f[1][0][0]=f[0][1][1]=1;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			f[i][j][0]=(f[i-1][j][0]+f[i-1][j][1])/2;
			f[i][j][1]=(f[i][j-1][0]+f[i][j-1][1])/2;
		}
	}
	printf("%.4lf",1-(f[n][n][0]+f[n][n][1]));
	return 0;
}

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