import math
isPrime = [True]*500005

# print(isPrime)

def makePrime():
  isPrime[0] = False
  isPrime[1] = False

  n = int(math.sqrt(500005))


  for i in range(2, n+1):
      if (not isPrime[i]):
          continue
      for j in range(i*2, 500005, i):
          isPrime[j] = False


makePrime()
p = []
N = int(input())
for i in range(2, N+1):
    if isPrime[i]:
        p.append(i)

# print(p)
ans = 0

for i in range(len(p)):
    for j in range(len(p)):
        t = p[i] * p[i] - p[j]
        if (t < 1 or t > N):
            break
        if (isPrime[t]):
            ans += 1

print(ans)