def isprime(p):
    if p <= 1:
        return False
    if p == 2:
        return True
    if p % 2 == 0:
        return False
    lim = int(p**0.5) + 1
    for q in range(3, lim, 2):
        if p % q == 0:
            return False
    return True


N = int(input())
ans = 2 if N >= 2 else 0
ans += sum(n for n in range(3, N + 1, 2) if isprime(n))
print(ans)