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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
int main()
{
    int x;
    while(scanf("%d",&x)!=EOF)
    {
        int i=0,j;
        while(1)
        {
            if(((1+i)*i)/2.0<x)
                i++;
            else if(((1+i)*i)/2.0==x)
            {
                printf("%d\n",i);
                break;
            }
            else if(((1+i)*i)/2.0>x)
            {
                break;
            }
        }
        for(j=i; j>0; j--)
        {
            if((((j-2)*(j-1))/2)+j==x)
            {
                printf("%d\n",j);
                break;
            }
        }
        for(j=i;; j++)
        {
            if(((j*(j+1))/2)-(j+1)==x)
            {
                printf("%d\n",j);
                break;
            }
        }
    }
    return 0;
}