The output of the program is 3.
Explanation:
Initially, a is assigned the value 0.
Since there's no case label matching a, the control jumps to default, where a is assigned 4.
Then, it goes to case 6, where a is decremented by 1 (a becomes 3).
Next, it goes to case 5, where a is incremented by 1 (a becomes 4).
Finally, it goes to case 1, where a is decremented by 1 (a becomes 3).
The value of a is printed, which is 3.