1042

#include<stdio.h>


int main(){
	int n,i;
	double sum;
	double fm; 
	double fz;
	scanf("%d",&n);
	fm=1.0;
	fz=1.0;
	sum=0.0;
	for(i=1;i<=n;i++)
	{
		sum+=i*fz/fm;
		fz=-fz;
		fm+=2;
	}
	
	printf("%.3f",sum);
	return 0;
}