import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();

        if(n == 1) {
            System.out.println(0);
            return;
        }
        int sum = 0;
        for(int i=2; i<=n; i++)
            sum += primeNum(i);

        System.out.println(sum);
    }

    public static int primeNum(int x) {
        boolean flag = true;
        for(int i=2; i<=x-1; i++) {
            if(x % i == 0) {
                flag = false;
                break;
            }
        }
        if(flag) return x;
        else return 0;
    }
}