The favourite 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 favourite 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 favourite prime numbers of Santa Claus.

Examples