#include<bits/stdc++.h>
using namespace std;
int n,sum;
int main(){
    cin>>n;
    int i=1;
    while(i<=n){
        sum+=i;
        i+=2;
    }
    cout<<sum;
    return 0;
}
/**************************************************************
	Problem: 1003
	User: wuweimo
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/