#!python
# -*- coding: utf-8 -*-


def is_sosuu(number):
    for i in range(2, int(number ** (1 / 2) + 1)):
        if number % i == 0:
            return False
    return True


def main():
    N = int(input())
    ANS = 0
    for n in range(2, N + 1):
        ANS += is_sosuu(n) * n
    print(ANS)


if __name__ == '__main__':
    main()