Prime Plus

Time Limit:1000MS  Memory Limit:65535KB
Description:
Write a program which reads an integer n and prints the number of prime numbers which are less than or equal to n. A prime number is a natural number which has exactly two distinct natural number divisors: 1 and itself. For example, the first four prime numbers are: 2, 3, 5, 7.
Input:
Input only has an integer n (0<n<100000001) in a line.
Output:
Prints the number of prime numbers.
Sample test:
Input
6
Output
3
Note:
Source:
Author:
ACSolo