#include <bits/stdc++.h> 
using namespace std;
int main(){
    int i=1,z,h=0;
    cin>>z;
    while(i<=z){
        h=h+i;
        i=i+2;
    }cout<<h;
}
/**************************************************************
	Problem: 1110
	User: xuezihong1
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/