Elevator Button Presses

You are given an elevator with a unique set of controls. The elevator has n floors, and the speed (or the number of button presses needed) for ascending each floor is given in an array of integers.

More specifically, you are given an integer n denoting the number of floors in the building, an array speeds of length n where speeds[i] denotes the number of button presses required to move from floor i+1 to floor i+2. You are also provided two integers s and t, representing the starting floor and target floor respectively. Your task is to compute the minimum total number of button presses needed to move from floor s to floor t (assuming s < t).

The computation is done simply by summing the speeds from floor s to floor t-1:

$$\text{result} = \sum_{i=s}^{t-1} speeds[i-1].$$

It is guaranteed that s is strictly less than t and that the inputs provided will follow these conditions.

inputFormat

The first line contains a single integer n representing the number of floors.

The second line contains n space-separated integers, where the i-th integer represents the speed (i.e., number of button presses) required to move from floor i to floor i+1.

The third line contains two space-separated integers: s (the starting floor) and t (the target floor), with s < t.

outputFormat

Output a single integer representing the total number of button presses required to move from floor s to floor t.

## sample

5
1 2 3 2 1
1 3

3