mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    N = int(input())

    is_prime = [1] * (N+1)
    is_prime[0] = 0
    is_prime[1] = 0
    ans = 0
    for i in range(2, N+1):
        if is_prime[i]:
            ans += i
            for j in range(2, N+1):
                if i * j <= N:
                    is_prime[i*j] = 0
                else:
                    break
    print(ans)


if __name__ == '__main__':
    main()