#define _USE_MATH_DEFINES
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include<iomanip>

//#include<bits/stdc++.h>



using namespace std;


bool F[10008];

int main() {

	long long int n,a=0,b=0;
	cin>>n;
	for(int i=1;i<=n;i+=2){
		if((n-i)/2==0)break;
		a+=((n-i)/2);
		////cout<<(n-1)/i;
	}
	for(int i=2;i<=n;i+=2){
		if((n-i-1)/2==0)break;
		a+=((n-i-1)/2);
		//cout<<"#"<<(n-3)/i;
	}
	cout<<a<<endl;
	return 0;
}