# No.713 素数の和
n = int(input())
primes = []

if n == 1:
    print(0)
elif n == 2:
    print(n)
else:
    for i in range(2, n + 1):
        for j in range(2, int(i ** 0.5) + 1):
            if i % j == 0:
                break
        else:
            primes.append(i)

    print(sum(primes))