#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin>>n;
	int s=0;
	int x=0;
	if(n%2==1)
	{
		for(int i=0;i<n;i++)
		{
			if(i%2==0)
			{
				s+=i;
			}
		}
		cout<<s;
	}
	else
	{
		for(int i=1;i<=n;i++)
		{
			if(n%i==0)
			{
				x+=i;
			}
		}
		cout<<x;
	}
	return 0;
}
/**************************************************************
	Problem: 1060
	User: chenkexin
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/