S : Cat nuke' Challenge

Problem tatement

Cat nuke i intereted in prime number and multiplication and ummation. Today, Cat nuke i playing with the operation involving all the $3$ thing he like.

Let $p_i$ $i$-th mallet prime number. For example, $p_1 = 2, p_2 = 3, p_3 = 5, ...$

You are given a poitive integer N. Calculate $\sum_{k=1}^{N-1} (p_k \times p_{k+1})$.

Contraint

• $1 ≤ N ≤ 1000$

ample Input 1

3

ample Output 1

21

$2 \times 3 + 3 \times 5 = 21.$