Counting Pairs with a Given Difference

Problem Description

Given a sequence of positive integers and a positive integer $C$, count the number of pairs satisfying $A - B = C$. Pairs whose values are the same but whose positions differ count as different pairs.

Input Format

The input has two lines.

The first line: two positive integers $N, C$.

The second line: $N$ positive integers $a_1, a_2, \ldots, a_N$ separated by spaces, the sequence to process.

Output Format

One line with an integer: the number of pairs satisfying $A - B = C$.

Sample Input

4 1
1 1 2 3

Sample Output

3

Sample Explanation

For the sample input, $N=4$, $C=1$, and the sequence is $1,1,2,3$. When $A=2$, the two $B=1$ values correspond to two pairs respectively; when $A=3$, $B=2$ corresponds to one pair. So there are $3$ pairs in total, and the output is $3$.

Constraints

For $75\%$ of the data, $1 \le N \le 2000$.

For $100\%$ of the data, $1 \le N \le 2 \times 10^5$, $0 \le a_i < 2^{30}$, $1 \le C < 2^{30}$.