#include<bits/stdc++.h>
using namespace std;
int main(){
    int n=1,s=1,h=0;
    cin>>n;
    while(s<=n){
        h+=s;
        s+=2;
         
    } 
    cout<<h;
    return 0;
}

/**************************************************************
	Problem: 1003
	User: lijinkai
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/