#include<bits/stdc++.h>
using namespace std;
int n,ans;
int main(){
    cin>>n;
    for(int i=1;i<=n;i+=2) ans+=i;
    cout<<ans;
    return 0;
}
/**************************************************************
	Problem: 1003
	User: wuhanyu
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/