#include <bits/stdc++.h>
using namespace std;
int main(){
    int n,p;
    cin>>n;
    p=sqrt(n);
    if(p==sqrt(n)){
    	cout<<p*p;
    }else{
    	p=(n-1)/2;
    	cout<<p*(p+1);
    }
}
/**************************************************************
	Problem: 1356
	User: wangyiyang
	Language: C++
	Result: Wrong Answer
****************************************************************/