Contiguous Subarray Sum

You are given an array of n integers and an integer k. Your task is to determine the number of contiguous subarrays that sum to exactly k.

A contiguous subarray is a sequence of elements from the array that occupy consecutive positions. Formally, for an array \(a\) of length \(n\), you need to count the number of pairs \((l, r)\) (with \(1 \leq l \leq r \leq n\)) such that:

\[ \sum_{i=l}^{r} a_i = k \]

Try to solve this problem efficiently.

inputFormat

The input is given via standard input (stdin) and has the following format:

• The first line contains two integers n and k, where n is the number of elements in the array and k is the target sum.
• The second line contains n space-separated integers representing the elements of the array.

outputFormat

Output a single integer on a new line: the number of contiguous subarrays whose elements sum to k.

## sample

5 7
3 4 7 2 -3

2