#include<bits/stdc++.h>
using namespace std;
int main(){
	int i,a,b=0,n,h=0;
	cin>>n;
	if(n%2==1){
		for(i=1;i<=n;i+=1){
			if(i%2==0){
				h=h+i;	
			}
	    }
		cout<<h;		
    }
    else{
    	for(a=1;a<=n;a++){
    		if(n/a==0){
    			b=b+a;
    		}
    	}
		cout<<b;	
    }
} 

/**************************************************************
	Problem: 1060
	User: hongjiaming
	Language: C++
	Result: Wrong Answer
****************************************************************/