from collections import defaultdict
from sys import stdin

def erastosthenes(n):
    prime = [0, 1] * ((n + 1) // 2)
    if not n % 2:
        prime += [0]
    prime[1], prime[2] = 0, 1

    i = 3
    while i <= n ** 0.5:
        for j in range(i * i, n + 1, i):
            prime[j] = 0
        i += 2
    return prime

def main():
    N = int(input())

    if N < 2:
        print(0)
        return

    lst = erastosthenes(N)
    primes = [2] + [i for i in range(3, N + 1, 2) if lst[i]]
    r2 = defaultdict(int)
    for i in primes:
        r2[i*i] = 1

    ans = 0
    for i in primes:
        if r2[2+i]:
            if i == 2:
                ans += 1
            else:
                ans += 2
    print(ans)

input = lambda: stdin.readline()
main()