Sequential Assembly Buffer

Parts arrive on a belt with unsorted integer IDs. They must be packed into boxes in strict sequential order starting from 1 (1, 2, 3...). If the part at the front of the belt is not the next one needed, it is moved to a holding buffer. Every time a part is packed, you must check the holding buffer to see if the next required part is now available there. Print the IDs in the order they are packed. Example: Input: 2 1 4 3 Output: 1 2 3 4