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

import numpy as np

N = int(read())

U = 5 * 10**5
is_prime = np.zeros(U,np.bool_)
is_prime[2] = 1
is_prime[3::2] = 1
for p in range(3,U,2):
    if p*p > U:
        break
    if is_prime[p]:
        is_prime[p*p::p+p] = 0

primes = np.where(is_prime)[0]

answer = 0
# (p,q,2)
if N >= 2:
    answer += 1
# (2,p,r) and (p,2,r)
primes = primes[primes <= N]
primes = primes[1:]
r = primes[primes**2 - 2 <= N]
answer += 2 * is_prime[r**2 - 2].sum()
print(answer)