It can be read upside down as well!

The numbers : I , $6 , 8 , 9 , 0$ are the only five numbers that can be read upside down as well.

Let the original number be $\overline{ABCDE}$ and the the upside down number be $\overline {FGHIJ}$

$\overline{ABCDE} - \overline {FGHIJ} = 78633$

Clearly $\overline{ABCDE}$ > 78633, so $A$ must be 8 or 9. We consider the two possibilities separately:

$A=9$ : Then $\overline{9BCDE}$ = 78633 + $\overline {FGHI6}$ , so $E=9$ . This implies $F=6$ , which is impossible, as 78633 + $\overline {FGHI6}$ would be a six-digit number.

$A=8$ : Then $\overline{8BCDE}$ = 78633 + $\overline {FGHI8}$ , so $E=1$ .

Now we know that the answer must have $A=8$ and $E=1$ , i.e.,
$\overline{8BCD1} - \overline{1GHI8} = 78633$ .

Note that $\overline{8BCD1} = 78633 + \overline{1GHI8} > 78633 + 10000 = 88633$ , so $B$ must be 8 or 9.

Since all the numbers are distinct ,thus $B=9$ : Then $\overline{89CD1} = 78633 + \overline{1GH68}$ , so $D=0$

Thus $C = 6$

The answer is $\boxed {89601}$