def num_prime(n):
    cnt = 0
    sup = n * ceil(log(n) + 2)
    if n == 1:
        return 2
    prime = [True] * sup
    prime[0] = prime[1] = False
    for i in range(2, sup):
        if not prime[i]:
            continue
        cnt += 1
        if cnt == n:
            return i
        for j in range(i * i, sup, i):
            prime[j] = False