import math

while True:
    try:
        n = int(input())
        c = [1 for i in range(n)]
        c[0] = 0
        i = 2
        while i**2 <= n:
            j = i*2
            while j <= n:
                c[j - 1] = 0
                j += i
            i += 1
        print(sum(c))
    except:
        break