def primes(N):
    #N = 5 * (10 ** 5)
    res = []
    isprime = [True] * (N + 1)
    isprime[0] = isprime[1] = False
    for i in range(2, N + 1):
        if isprime[i]:
            res.append(i)
            for j in range(i * 2, N + 1, i):
                isprime[j] = False
    return res

N = int(input())
P = primes(N)
#print(len(P))
S = set([r * r for r in P])
ans = 0
for q in P:
    q2 = q + 2
    if q2 in S:
        ans += 1
print(ans * 2 - 1)