It keeps saying that my program produces incorrect solutions. Anyone else is having the same issue?

#include <stdlib.h>
#include <stdio.h>

int main() {
  int start, change, N, sum;
  scanf("%d", &N);
  if (abs(N) <= 10000) {
    change = N > 1 ? 1 : -1;
    for (start = 1; start != (N + change); start += change)
      sum += start;
    printf("%d\n", sum);
  }
  return 0;
}