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Velma and Triplets
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Ad-Hoc, Combinatorics, Easy, Implementation, Math, Medium

Problem
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Given an array of size N, Velma give Scooby and Shaggy to compute the following sum on the array (0-indexed array).
enter image description here,
where $$\lfloor.\rfloor$$ is the floor operator.
Since it was taking too long for Scooby and Shaggy to compute the sum, they need your help.
Can you help them?

Input

The first line of input will contain a single integer N, denoting the size of the array.
The second line will contain N integers arr0, arr1, arr2, ..., arrn-1.

Output

Print a single integer, the answer to Velma's question.

Constraints

  • $$ 1 \leq N \leq 100, 1 \leq arr_{i} \leq 1000 $$ in 40% of test cases.
  • $$ 1 \leq N \leq 3 \cdot 10^5, 1 \leq arr_{i} \leq 5*10^4 $$ in 60% of test cases.

Note: The answer will fit in signed 64-bit integer

SAMPLE INPUT
5
1 2 1 7 3
SAMPLE OUTPUT
6
Explanation

The following triplets exists in the given array:
1 2 1
1 2 7
1 2 3
1 1 7
1 1 3
1 7 3
2 1 7
2 1 3
2 7 3
1 7 3
So, if we compute the required sum using these triplets, we get the sum to be equal to 6.

Time Limit: 1.0 sec(s) for each input file.
Memory Limit: 256 MB
Source Limit: 1024 KB
Marking Scheme: Marks are awarded when all the testcases pass.
Allowed Languages: C, C++, Clojure, C#, D, Erlang, F#, Go, Groovy, Haskell, Java, Java 8, JavaScript(Rhino), JavaScript(Node.js), Lisp, Lisp (SBCL), Lua, Objective-C, OCaml, Octave, Pascal, Perl, PHP, Python, Python 3, R(RScript), Racket, Ruby, Rust, Scala, Scala 2.11.8, Swift, Visual Basic

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This Problem was Asked in

HackerEarth

Challenge Name

October Circuits

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