# The staircase

# The staircase

At each of the **n** + **2** steps of the staircase an integer is written, on the first and last step there is a number **0**. The man stands on the first step. He must climb the last step. In one step, he can rise any number of steps not greater than **k**.

Find the sum of all the numbers written on the steps, which came a man. Find the largest possible value of this amount.

**Input **

The first line contains the number **n** (**0** ≤ **n** ≤ **1000**). On the second line **n** integers written on the steps are given (except on the first and the last step, which contain zero). They do not exceed **1000** by absolute value and are separated by spaces. The maximum length of the man's step **k** (**1** ≤ **k** ≤ **n**) is given in the third line. **Output**

Print the greatest possible sum of numbers written on the steps, which passed the man.

3 1 -1 1 2

2