#yuki843
import sys

x=int(raw_input())
if x<2:
 print 0
 sys.exit()
def prime_list(x):
 pl=[2]
 for i in range(3,x+1):
  for j in pl:
   if j*j>i:
    pl.append(i)
    break
   if i%j==0:
    break
 return pl

p=prime_list(x)
s=set(p)
res=1
for i in p[1:]:
 if i*i-2 in s:
  res+=2
print res