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 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define _GLIBCXX_DEBUG
#define PI 3.1415926535897932
#define MOD 1000000007;
using namespace std;
long long GCD(long long A,long long B){
  if(B==0){
    return A;
  }
  else{
    return GCD(B,A%B);
  }
}
long long LCM(long long A,long long B){
  long long g=GCD(A,B);
  return A/g*B;
}
long long num_order(long long X){
  long long ans=0;
  while(true){
    if(X==0){
      break;
    }
    else{
      X/=10;
      ans++;
    }
  }
  return ans;
}
int main() {
  
  int X;
  cin>>X;
  
  int i=0;
  
  int sum=0;
  
  
  while(sum<X){
    i++;
    sum+=i;
  }
  
  
  cout<<i<<endl;
}