#include<bits/stdc++.h>
using namespace std;
int main(){
    int n=0,c=0,b=1;
    cin>>n;
    while(b<=n){
    c=b+c;
    b=b+2;
    }
    cout<<c;
    }
/**************************************************************
	Problem: 1110
	User: binzicheng1
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/