Pairs within budget

Problem

A shop has n gifts with known prices. Count the pairs of different gifts whose prices add up to at most X.

Example 1

Input

5 6
1 5 3 4 2

Output

Six pairs fit.

Example 2

Input

2 1
1 1

Output

Try the problem first. Open one hint at a time.

Hint 1

Sort the prices, then keep one pointer at each end.

Hint 2

When the smallest and largest fit together, the smallest fits with every price between them.

Write your Python code, run it on the examples and submit it to hidden tests.