LIMIT = 10000000
 
isPrime = [True for _ in range(LIMIT)]

isPrime[0] = isPrime[1] = False
 
for i in range(2, int(LIMIT ** 0.5)+1):
  if isPrime[i]:
    for j in range(i * i, LIMIT, i):
      isPrime[j] = False
 
try:
    while True:
        n = int(input())
        count = 0
        for i in range(n+1):
            if isPrime[i]:
                count += 1
        print(count)
except EOFError:
  pass