Help needed in this Dp Problem

Problem - C - Codeforces

there must be a positive integer k (1 ≤ kn - 1) such that t 1 < 0, t 2 < 0, …, t k < 0 and t k + 1 > 0, t k + 2 > 0, …, t n > 0. In particular, the temperature should never be zero. If this condition is not met, Vasya decides that his city has environmental problems, and gets upset.

You do not want to upset Vasya. Therefore, you want to select multiple values of temperature and modify them to satisfy Vasya’s condition. You need to know what the least number of temperature values needs to be changed for that.

problem main crux i copied from the problem please help What shall be the approach for this problem