#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,i,h=0;
    cin>>n;
    for(i=1;i<=n;i+=2){
        h=h+i;
    }
    cout<<h;
}
/**************************************************************
	Problem: 1110
	User: wengzihang
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/