#include <stdio.h>
#include <stdlib.h> 
#include <string.h>
#include <math.h>
#include <iostream>
#include <vector>

using namespace std;
 
int main(){
	int n;scanf("%d",&n);
	double a=4,a1=3,a2;
	if(n==0){
		printf("4\n");return 0;
	}
	else if(n==1){
		printf("3\n");return 0;
	}
	
	for(int i=2;i<=n;i++){
		a2=(19/4.0*a1-3.0*a);
		a=a1;
		a1=a2;
		if(a2<(double)1e-9){
			a2=0;
			break;
		}
	}
	if(a2==0)printf("0\n");
	else printf("%0.10f\n",a2);
	//else printf("%0.10f\n",a2);
	
	return 0;
}