Strange Grid

A strange grid has been recovered from an old book. It has 5 columns and infinite number of rows. The bottom row is considered as the first row. First few rows of the grid are like this:

…………..

…………..

20 22 24 26 28

11 13 15 17 19

10 12 14 16 18

1 3 5 7 9

0 2 4 6 8

The grid grows upwards forever!

Your task is to find the integer in cth column in rth row of the grid.

Input Format

There will be two integers r and c separated by a single space.

Constraints

1≤r≤2 * 109

1≤c≤5

Rows are indexed from bottom to top and columns are indexed from left to right.

Output Format

Output the answer in a single line.

Sample Input

6 3

Sample Output

25

Explanation

The number in the 6th row and 3rd column is 25.

#include <stdio.h>

#include <string.h>

#include <math.h>

#include <stdlib.h>

int main() {
    long long  int r,c,num;
    scanf("%lld%lld",&r,&c);
    if(r%2 == 0)
        {
        num =   10*((r/2)-1)+1;
        num = num + 2*(c-1);
    }
    else
        {
        num =   10*(r/2);
        num = num + 2*(c-1);        
    }
    printf("%lld\n",num);
    return 0;
}

Compile & Run : https://ideone.com/cp30GN