Lia is fascinated by anything she considers to be a twin. She calls a pairs of positive integers, $\boldsymbol{i}$ and $j$, twins if:

They are both prime. A prime number is an integer greater than $\mbox{1}$ that has no positive divisors other than $\mbox{1}$ and itself.

Their absolute difference is exactly equal to $2$ (i.e., $|j-i|=2$).

Given an inclusive interval of integers from $n$ to $m$, can you help Lia find the number of pairs of twins there are in the interval (i.e., $[n,m]$)? Note that pairs $(i,j)$ and $(j,i)$ are considered to be the same pair.

Input Format

Two space-separated integers describing the respective values of $n$ and $m$.

Constraints

$1\leq n\leq m\leq10^9$
$m-n\leq10^6$

Output Format

Print a single integer denoting the number of pairs of twins.

Sample Input 0
3 13

Sample Output 0
3

Explanation 0

There are three pairs of twins: $(3,5),(5,7)$, and $(11,13)$.

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