Permutations on the Road: Alice

아직 제출이 없습니다시간 제한3초메모리 제한1024 MB

문제

Alice and Bob frequently take long road trips to get to various programming competitions in their area. Since everything's bigger in the state that they live in, they have turned to playing car games to pass the time.

Alice and Bob are both computer scientists, so they quickly tired of "guess the number", as the guesser could always identify the number using a logarithmic number of guesses. To up the challenge, they created a new game: "guess the permutation".

A permutation of length NN is an arrangement of the numbers 1,,N1, \dots, N. For a given permutation PP, define inv(l,r)\text{inv}(l, r) to be the number of pairs (i,j)(i, j) with lijrl \leq i \leq j \leq r such that P_i>P_jP\_i > P\_j.

When playing this game, Alice thinks of a permutation, and Bob can ask Alice the result of the function inv\text{inv} for up to NN inputs. 

Alice has already thought of her permutation PP. As she mindlessly answers all of Bob's queries, she thinks of a different problem: What is the sum of inv(l,r)\text{inv}(l, r) over all values of ll and rr?

입력

The first line of input contains a single integer NN (1N100,0001 \leq N \leq 100\\,000), the length of the permutation. The second line of input contains NN space separated integers, Alice's permutation PP.

출력

Output a single integer, the sum of inv(l,r)\text{inv}(l, r) over all values of ll and rr. It is guaranteed the answer fits in a signed 6464-bit integer.

힌트

In the first sample case, there are no inversions.

In the second sample case,

  • inv(1,1)=0\text{inv}(1, 1) = 0.
  • inv(1,2)=0\text{inv}(1, 2) = 0.
  • inv(1,3)=1\text{inv}(1, 3) = 1.
  • inv(2,2)=0\text{inv}(2, 2) = 0.
  • inv(2,3)=1\text{inv}(2, 3) = 1.
  • inv(3,3)=0\text{inv}(3, 3) = 0.

Summing these values gives 22.