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