Append the next sentence to the given sentence in a grammatically correct manner.
I was so tired that
I was so tired that I could barely keep my eyes open.
Complete the following task based on the instruction and optional input provided.### Instruction:
Append the next sentence to the given sentence in a grammatically correct manner.

### Input:
I was so tired that

### Output:
I was so tired that I could barely keep my eyes open.