#include <stdio.h>

// 1 2 3 4 2 4 6 0 12

int main(void){
    int b[] = {1, 2, 3, 4, 2, 4, 6, 0, 12};
    printf("%u\n", normalChecksum(b, 9));
    return 0;
}


int normalChecksum(int *b, int n){
  int i;
  int a, bb;

  for(i = 1, a = 0; i < n; i++)
    a+=(int)b[i];

  bb = a / 256;
  a = (a - 256 * bb) + bb;
  bb = a / 256;

  return (int)((a-256*bb)+bb);
}