Problem Statement

AtCoDeer has an empty piggy bank.
On the morning of the i-th day, he will put i yen (Japanese currency) in it: 1 yen on the morning of the 1-st day, 2 yen on the morning of the 2-nd day, and so on.
Each night, he will check the amount of money in it.
On which day will he find out that his piggy bank has N yen or more for the first time?

Input

Input is given from Standard Input in the following format:
N

Output

Print an integer x such that AtCoDeer will find out that his piggy bank has N yen or more for the first time on the x-th day.

Constraints

• $1 \le N \le 10^9$
• N is an integer.

Sample Input 1

12

Sample Output 1

5

• On the 1-st day, the piggy bank gets 1 yen in the morning and has 1 yen at night.
• On the 2-st day, the piggy bank gets 2 yen in the morning and has 3 yen at night.
• On the 3-rd day, the piggy bank gets 3 yen in the morning and has 6 yen at night.
• On the 4-th day, the piggy bank gets 4 yen in the morning and has 10 yen at night.
• On the 5-th day, the piggy bank gets 5 yen in the morning and has 15 yen at night.

Thus, on the 5-th night, AtCoDeer will find out that his piggy bank has 12 yen or more for the first time.

Sample Input 2

100128

Sample Output 2

447

见题面 Input 部分

见题面 Output 部分