Roy and Rangoli

4.2

10 votes
Approved, Implementation, Math, Medium, Open, Primality test
Problem

Its Diwali time and little Roy thought of an interesting design for Rangoli. He created an N x N grid. Roy fills some of the cells of grid with red color.

Cell located at ith row and jth column is colored if i+j is prime. Consider Zero-based numbering of grid. (See Sample Test Case Explanation for clarification)

Roy wants to know how many cells he will have to color given the size of grid N.

Input:

One integer indicating size of grid N

Output:

Print a single integer, number of cells Roy will have to color. Since answer can be very large output it modulo 1000000007

Constraints:

1<= N <=1000000

Sample Test Case Explanation:

enter image description here

Time Limit: 3
Memory Limit: 256
Source Limit:
Explanation

As shown in the image above, five cells (0,2), (1,1), (1,2), (2,0), (2,1) are colored red because for (i,j) i+j for these cells results into a prime number.

Editor Image

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