小於N的質數個數

 #小於N的質數個數

while True:

try:

n = int(input())

d = list(range(n))

d[1]=0

for i in range(2,int(n**0.5)+1):

  for j in range(i**2,n,i):

    d[j]=0

d1 = [ i for i in d if i!=0]

print(len(d1))

except:

break