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 Fortran (GNU Fortran 9.2.1) (judge verdict: Accepted)

program sample
    implicit none
    character(100)::s,t
    integer(8) :: i,j,k,m,n,ans
    integer(8)::a,b,c,d
    integer(8),allocatable::x(:),y(:)
  
    read(*,*)k
    do i=1,k/2+1
        m=m+i
        if(m>=k)then
            
            ans=i
            
            write(*,*)ans
            stop
        end if
    end do       
    
    stop
end program sample