from itertools import count
def primes():
    g = count(2)
    while True:
        p = next(g)
        yield p
        g = filter(lambda n,p = p:n % p,g)


N = int(input())
prime = primes()
psum=0
for p in prime:
    if N < p:
        break
    psum+=p
print(psum)