#include <bits/stdc++.h>
using namespace std;
int main(){
    int i,n=0;
    cin>>i;
    if(i%2==1){
        for(int k=2;k<i;k+=2)n+=k;
    }else{
        for(int k=1;k<=i;k++){
            if(i%k==0)sum+=k;
        }
    }
    cout<<n;
}
/**************************************************************
	Problem: 1060
	User: yangjunwen
	Language: C++
	Result: Compile Error
****************************************************************/