#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    
    if (n % 2 == 1) {
        // 计算1到n之间所有偶数的和
        int sum = 0;
        for (int i = 2; i < n; i += 2) {
            sum += i;
        }
        cout << sum << endl;
    } else {
        // 计算n的所有约数之和
        int sum = 0;
        for (int i = 1; i <= n; i++) {
            if (n % i == 0) {
                sum += i;
            }
        }
        cout << sum << endl;
    }
    
    return 0;
}

/**************************************************************
	Problem: 1060
	User: fuyijun
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/