Derive and simplify the expression for the number of times step 5 is executed? Use proper notation, similar to page 26 of text, as defined in class. Give the worst-case running time. Assume the cost (c term) is 1 for all steps.

function problem1 (n)

1. r = 0;

2. for i := 1 to n-1 do

3. for j = 1 to i do

4. for k = j+1 to n do

5. r++;

6. return (r);