```
#include <stdio.h>
#include <cs50.h>
#include <math.h>
int main (void) {
///Get correct user input
printf("Number:");
long long number = get_long_long();
if (number<0) {
printf("Must be positive, retry: ");
number = get_long_long();
}
///Counting numbers in card
int counter = 1;
long long characters = number;
do {
characters = characters/10;
counter = counter+1;
} while (characters>1);
///So original long long can be used if needed
int digits = round(number);
//validity algorithms go heree
int a = 0;
int i;
int k;
int q;
int z = 0;
int n;
/// a is every other nunber * 2
for (i=1; i<counter; i++) {
for (n=0; n<1; n++) {
k = pow(10,2*i);
q = pow(10, 2*i-1);
z = (digits%k-digits%q)/q;
z = z*2;
if (z >= 10) {
z = z%10 + 1;
}
}
a = a + z;
///if statement here for if the number is two digit//
}
```