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Time Limit: 2 sec / Memory Limit: 256 MB

• X は整数
• 1≦X≦10^9

### 入力

X


### 出力

カンガルーが座標 X に到着する時刻の最小値を出力せよ。

### 入力例 1

6


### 出力例 1

3


3 回右にジャンプすると時刻 3 に家にたどり着けて、これが最小です。

### 入力例 2

2


### 出力例 2

2


### 入力例 3

11


### 出力例 3

5


Score : 200 points

### Problem Statement

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 1

6


### Sample Output 1

3


The kangaroo can reach his nest at time 3 by jumping to the right three times, which is the earliest possible time.

### Sample Input 2

2


### Sample Output 2

2


He can reach his nest at time 2 by staying at his position during the first second, and jumping to the right at the next second.

### Sample Input 3

11


### Sample Output 3

5