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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
public class Aprob {
    public static void Main() {
        int X = int.Parse(Console.ReadLine());
        int X2 = X;
        int count = 0;
        for (int i = 1; true; i++) {
            X -= i;
            if (X > 0) {
                count++;
            } else if (X == 0) {
                count++;
                break;
            } else {
                X += i;
                X += i - 1;
                count += X - (i - 1);
                break;
            }
        }
        int count2 = 0;
        for (int i = 1; true; i++) {
            X2 -= i;
            if (X2 > 0) {
                count2++;
            } else {
                count2++;
                break;
            }
        }
        count2 += (X2 * -2);
        Console.WriteLine(Math.Min(count,count2));
    }
}