A monkey types a 280-character message on Twitter, using only the 26 upper-case English letters. A research assistant is trying to determine if there is any hidden meaning in the message, and tries partitioning the message into 3 segments (the first $x$ letters, the next $y$ letters, and the last $280-x-y$ letters). How many ways could the message be partitioned, assuming each segment has at least one letter?
Attempt at solution:
I was wondering partition 1 would have one character - 1 character, partition 2 would have 1 letter (-1 character) and the third parse would have two letters because they would have x and y (-2 characters). Would it be then 276 distingusible objects (the characters) over 3 distinguishable boxes (the parsese)?