求调，用的是线性筛

def isprime(n,status_d):
   anslist=[]
   pr=1
   for i in range(2,n+1):
      if status_d[i]:
         anslist.append(i)
      for pj in anslist:
         if i*pj>n:
            break    # i*pj 超范围，退出循环
         if i%pj==0:
            status_d[int(i * pj)]=False
            break
         else:
            status_d[int(i * pj)]=False
   return anslist

n=int(input())
status_d=[True]*(n+1)
status_d[0]=status_d[1]=False

anslist=isprime(n,status_d)
print(len(anslist))