题目描述
There is a kangaroo at coordinate 0 on an infinite number line that runs from left to right, at time 0.
During the period between time i-1 and time i, the kangaroo can either stay at his position, or perform a jump of length exactly i to the left or to the right.
That is, if his coordinate at time i-1 is x, he can be at coordinate x-i, x or x+i at time i.
The kangaroo's nest is at coordinate X, and he wants to travel to coordinate X as fast as possible.
Find the earliest possible time to reach coordinate X.
-----Constraints-----
- X is an integer.
- 1≤X≤10^9
-----Input-----
The input is given from Standard Input in the following format:
X
-----Output-----
Print the earliest possible time for the kangaroo to reach coordinate X.
-----Sample Input-----
6
-----Sample Output-----
3
The kangaroo can reach his nest at time 3 by jumping to the right three times, which is the earliest possible time.
输入格式
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输出格式
见题面