#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin >> n ;
    cout << (1+n)*((n-1)/2+1)/2;
    return 0;
  
}
/**************************************************************
	Problem: 1003
	User: suziqian
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/