Educational Codeforces Round 34 (Rated for Div. 2) D

D. Almost Difference

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Let's denote a function

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.

Examples

input

51 2 3 1 3

output

4

input

46 6 5 5

output

0

input

46 6 4 4

output

-8

题意就是计算那个方程的和

比赛时我推了一下公式，没想到会爆long long最后被hack QAQ

观摩一下大神的代码要用long double存Orz

#include <stdio.h>#include <iostream>#include <algorithm>#include <string.h>#include <math.h>#include <map>#include <iomanip>using namespace std;typedef long long ll;ll a[200005];map<ll,ll> m;int main(){ll n; cin>>n;m.clear();for(ll i=0;i<n;i++){cin>>a[i];}long double sum=0,ans=0;for(ll i=0;i<n;i++){ll s=i*a[i]-sum+m[a[i]+1]-m[a[i]-1];//ans+=((i-m[a[i]-1]-m[a[i]+1]-m[a[i]])*a[i]-(sum-m[a[i]+1]*(a[i]+1)-m[a[i]-1]*(a[i]-1)-m[a[i]]*a[i]));ans+=s;m[a[i]]++;sum+=a[i];}cout<<fixed<<setprecision(0)<<ans<<endl;return 0;}