// External Function (prototype)
printf(fmt, args);
atoi(str);

// factorial function
fact(n) {
  if (n == 0) return 1;
  else return n*fact(n-1);
}

// Main routine
main(argc, argv) {
  var n;

  if (argc < 2) {
    printf("usage: facto n\n");
    return 1;
  }

  n = atoi(argv[1]);
  printf("%d! = %d\n", n, fact(n));
  return 0;
}