#include <iostream>
#include<stdio.h>
int main() {
	// your code goes here
	int d,ans=0;
	
	std::cin>>d;
	for(int x=1;x*2+2<=d;x++){
		int y=(d-2*x)/2;
		if(y<x)break;
		if(x*y>ans)ans=x*y;
	}
	printf("%d\n",ans);
	return 0;
}