#include<bits/stdc++.h>
using namespace std;
int a,b,c,d,k,f;
int main(){
    cin>>a;
    for(int i=1;i<=a;i=i+2){
        f=f+i; 
    }
    cout<<f; 
}
/**************************************************************
	Problem: 1110
	User: wangyousi
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/