# coding: utf-8
# Your code here!

n=int(input())
if n==1: print(0); exit()



def Eratosthenes(N):
    N+=1
    is_prime_list = [True]*N
    is_prime_list[0], is_prime_list[1] = False, False
    for j in range(4,N,2): is_prime_list[j] = False
    m = min(int(N**0.5)+10,N)
    for i in range(3,m,2):
        if is_prime_list[i]:
            for j in range(i*i,N,i):
                is_prime_list[j] = False
    return [number for number, TF in enumerate(is_prime_list) if TF]

heiho = {i*i for i in Eratosthenes(n)}

ans = 0
for i in Eratosthenes(n+1):
    if i+2 in heiho:
        ans += 1
#        print(i)

print(ans*2-1)