How to calculate sum of time difference

Hi
I have a start and end time column and in the next column (C) I’m calculating time difference. Now I need the total of time diff. But the problem is if the total in more than 24hr excel automatically changing the time to next day,
For example in column C I’ve following time difference

09:00:00
06:30:00
11:00:00
I want the total which is 26:30:00. But excel showing it as 02:30:00 which is 2:30 AM of next day time. How do I get the total value??