Given an array of non-positive integers of length $$$n$$$ $$$(1 \leq n \leq 10^5)$$$ i.e. $$$a_i \leq 0$$$. $$$(-10^9 \leq a_i \leq 0)$$$ We want to make all elements equal to $$$0$$$. We can do the following operation any number of times (possibly zero).

Choose any subarray and increase all its elements by $$$1$$$.

What is the minimum number of operations to make all elements equal to $$$0$$$?

Input

7

0 -1 -1 -1 0 -2 -1

Output

3