题目描述

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.

输入描述

Input only has an integer n (0<n<100000001) in a line.

输出描述

Prints the number of prime numbers.

示例

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