def isPrime(N):
	isp=[True for _ in range(N+1)]
	isp[0],isp[1]=False,False
	for i in range(2,N+1):
		if i*i>N:
			break
		for j in range(2,N+1):
			if i*j>N:
				break
			isp[i*j]=False
	return isp

def main():
	N=int(input())

	isp=isPrime(N)

	ans=0
	for r in range(2,N+1):
		if isp[r]==False:
			continue
		if r*r-2<=N and isp[r*r-2]==True:
			ans+=2
			if r==2:
				ans-=1
	
	print(ans)
	return

main()