C++ :

#include <iostream>
using namespace std;
 
int main(){ 
    int n,s=0,i=0;
    cin>>n;
    
    while(s<n){
    	i++;
    	s+=i;	
	}
	cout<<i<<endl;
}

Pascal :

program liumohan;
var a,b,i,c,s:longint;
begin
  read(a);
  for i:=1 to a do
  for c:=1 to i do
  begin
  s:=s+1;
  if s=a then begin writeln(i); halt; end;
  end;
  end.

Java :

import java.util.Scanner;
public class Main{
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int n=in.nextInt();
		for(int i=1;i<100;i++){
			if((1+i)*i/2>=n){
				System.out.println(i);
				break;
			}
			
		}
	}

}

Python :

n = int(input())
t = []
for i in range(1, n + 1):
    for j in range(1, i + 1):
        t.append(i)
print(t[n - 1])