Prime sum | Practice Problems

Prime sum

★★★★★

4 votes

Special Numbers, Counting, Implementation, Math Basic, Basic Programming, Basic Math, Basics of Implementation, Sieve, Math

Details

Problem

You are given a number $N$ . Find all pairs of prime numbers $(L,R)$ such that $L ≤ R$ and their sum is also a prime number and no more $N$ .

Input format

The first line contains a single integer $N$ .

Output format

The single integer is the number of pairs that satisfy the condition.

Constraints

$1 ≤ N ≤ 10^7$

Time Limit: 1

Memory Limit: 256

Source Limit:

Explanation

If first case is one pair ( $L,R$ ) which suits us - $(2,3)$ , because $2 + 3 = 5$ , $5$ - prime number.