#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b,c=0;
    cin>>a;
    for(b=1;b<=a;b+=2){
        c=c+b;
    }
    cout<<c;
}
/**************************************************************
	Problem: 1110
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/