import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

import numpy as np

N = int(read())

def make_prime(U):
    is_prime = np.zeros(U,np.bool)
    is_prime[2] = 1
    is_prime[3::2] = 1
    M = int(U**.5)+1
    for p in range(3,M,2):
        if is_prime[p]:
            is_prime[p*p::p+p] = 0
    return is_prime, is_prime.nonzero()[0]

is_prime, primes = make_prime(N+1)
answer = primes.sum()
print(answer)