You are given a permutation $A$ of length $n$. In one operation, you can select 2 adjacent elements $A_i$ and $A_{i + 1}$ and swap them. Find the minimum number of operations required to sort the permutation in ascending order.
### Input
- The first line contains an integer $n$.
- The second line contains $n$ integers $A_i$.
### Output
- Print the number of operations required.
### Constraints
- $1 \le n \le 10^5$.
### Example
Input:
```
4
2 4 1 3
```
Output:
```
3
```
