#include <stdlib.h>
#include <ctype.h>

long atol(const char* s) {
  long n = 0;
  int neg = 0;
  while (isspace(*s))
    s++;
  switch (*s) {
    case '-':
      neg = 1;
    case '+':
      s++;
  }
  /* Compute n as a negative number to avoid overflow on LONG_MIN */
  while (isdigit(*s))
    n = 10 * n - (*s++ - '0');
  return neg ? n : -n;
}