'''
Online Python Compiler.
Code, Compile, Run and Debug python program online.
Write your code in this editor and press "Run" button to execute it.
'''
import random
x=0
y=0
z=0
n=0
limit=7*60*10
while n<limit:
x=random.randint(1,20)
if x==20:
y=1
n=n+1
while n<limit and y==1:
x=random.randint(1,20)
if x==20:
z+=1
if x==1 or x==2 or x==3 or x==4 or x==5:
y=0
n+=1
print (z)