import math

def get_prime(n):
    if n <= 1:
        return []
    prime = [2]    
    limit = int(math.sqrt(n))

    data = [i for i in range(3,n,2)]
    
    while limit > data[0]:
        prime.append(data[0])
        data = [i for i in data if i%data[0] != 0]

    return prime + data
    
n = int(input())

print(sum(get_prime(n)))