Problem:
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

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;

public class Main { // "Main" should be used for most online judges
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int nestValue = sc.nextInt();
		int result = 0;
		
		for (int i = 0; i <= nestValue; i++) {
			if(maxValue(i) >= nestValue) {
				result = i;
				 i = nestValue;
			}
		}
		
		System.out.println(result);
		sc.close();
	}
	
	public static int maxValue(int n) {
		int max = 0;
		for (int i = 1; i <= n; i++) {
			max += i;
		}
		return max;
	}
}