Count Primes in an Interval

Source: Phước Hưng OJ

Version: Phuoc Hung OJ Extended

Problem Statement

Given $0\le L\le R\le20000$, count primes in the inclusive interval $[L,R]$. A prime is an integer greater than 1 with exactly two positive divisors. Neither 0 nor 1 is prime. Use direct trial division; a sieve or array is unnecessary.

Input

One line contains integers $L,R$.

Output

Print the number of primes in the inclusive interval.

Subtasks

• Subtask 1 (20%): $0\le L\le R\le 100$.

• Subtask 2 (30%): $0\le L\le R\le 2000$.

• Subtask 3 (50%): $0\le L\le R\le 20000$.

Examples

Example 1

Input:

0 10

Output:

4

Explanation:

Count only numbers at least 2 with no divisor up to their square root.

Example 2

Input:

1 1

Output:

0

Explanation:

Count only numbers at least 2 with no divisor up to their square root.