def getprim(n):
    N = 1000000+10
    prime, isp = [], [1]*N

    for i in range(2, n+1):
        if isp[i]: prime.append(i)
        j = 0
        while i * prime[j] <= n:
            isp[i * prime[j]] = 0
            if i % prime[j] == 0: break
            j+=1

    return len(prime)

n = int(input())
print(getprim(n))