public int sum67(int[] nums) {
  int sum = 0;
  for (int i = 0; i < nums.length; i++) {
    int n = nums[i];
    if (n == 6) {
      i++;
      while (i < nums.length && nums[i] != 7) {
        i++;
      }
    }
    else {
      sum += n;
    }
  }
  return sum;
}