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++ (Clang 10.0.0) (judge verdict: Accepted)

/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author
 */

#include <iostream>
#include <fstream>

#include <iostream>
#include <string>
#include <vector>
#include <math.h>
#include <map>
#include <set>
#include <algorithm>
#include <numeric>
#include <bitset>
using namespace std;
using ll = long long;
constexpr ll INF = 1010000000000000017LL;
#define rep(i, n) for(ll i = 0; i < (ll)(n); i++)
#define all(v) v.begin(), v.end()

class CGoHome {
public:
	void solve(std::istream& in, std::ostream& out) {
        ll x;
        in>>x;

        rep(i,50000){
            if(x<=i*(i+1)/2){
                out<<i<<endl;
                return;
            }
        }

	}
};


int main() {
	CGoHome solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
	solver.solve(in, out);
	return 0;
}