题目描述
Let's denote a function
$$d(x,y) = \begin{cases} y - x, & \text{if } |x-y| > 1 \\ 0, & \text{if } |x-y| \leq 1 \end{cases}$$
You are given an array a consisting of n integers. You have to calculate the sum of d(ai, aj) over all pairs (i, j) such that 1 ≤ i ≤ j ≤ n.
Input
The first line contains one integer n (1 ≤ n ≤ 200000) — the number of elements in a.
The second line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 109) — elements of the array.
Output
Print one integer — the sum of d(ai, aj) over all pairs (i, j) such that 1 ≤ i ≤ j ≤ n.
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分
样例输入
5
1 2 3 1 3
样例输出
4
提示
In the first example:
- d(a1, a2) = 0;
- d(a1, a3) = 2;
- d(a1, a4) = 0;
- d(a1, a5) = 2;
- d(a2, a3) = 0;
- d(a2, a4) = 0;
- d(a2, a5) = 0;
- d(a3, a4) = - 2;
- d(a3, a5) = 0;
- d(a4, a5) = 2.