Problems

# The favorite numbers of Santa Claus

# The favorite numbers of Santa Claus

Santa Claus liked play with numbers and figures. Most of all he liked a number **1** because **1.01** New Year starts.

Years passed, but he stayed be of superstitious - he didn't like numbers, where **3** stand after **1**, that is number **13**. On New Year he decided to give a new problem: count how many Santa Claus favorite prime numbers contains the interval [**a**, **b**]?

#### Input

Contains two numbers: the start **a** and the end **b** of the interval (**1** ≤ **a** ≤ **b** ≤ **500000**).

#### Output

Print the amount of favorite prime numbers of Santa Claus.

Input example #1

9 23

Output example #1

4