The problem:

Starting with the number 1 and moving to the right in a clockwise direction a 5 by 5 spiral is formed as follows:

21 22 23 24 25
20  7  8  9 10
19  6  1  2 11
18  5  4  3 12
17 16 15 14 13

It can be verified that the sum of the numbers on the diagonals is 101.

What is the sum of the numbers on the diagonals in a 1001 by 1001 spiral formed in the same way?

My solution

#include <stdio.h>

int main(){
  int i,j;
  int soma=1;
  int inicio,diferencial;

  inicio=1;
  diferencial=2;
  for (i=3;i<=1001;i+=2){

    for (j=1;j<5;j++){
      inicio+=diferencial;      
      soma+=inicio;      
    }
    diferencial+=2;
  }
        
  printf("%d\n",soma);
return 0;
}