import java.io.*;
public class Triangular {
    public static boolean triangular(int number)
    { 
        if (number < 1) return false; // only positive numbers
 
        int tri = 0;
        for (int i=1; tri<number; ++i)
        { 
            tri += i; // create next triangular number
        }   // after the for-loop, tri>=number, with
            // tri==number if number is triangular and
            // tri>number if number is not triangular
 
        return (tri==number);
    }
 
 
    public static void main(String[]args) {
        
 
        //Ask user to supply a number
        int userInput = getInput("Please enter a number to see if it is a Triangular Number>");
        System.out.println("The number you entered is " + userInput);
        System.out.println("The number " + (triangular(userInput) ? "is " : "is not ") + "a triangular number" );
 
    }
    
    public static int getInput(String message){
        int n = -1;
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            System.out.println(message);
            String s = br.readLine();
            n = Integer.parseInt(s);
        }catch(IOException ioe){
            System.err.println(ioe.getMessage());
        }catch(NumberFormatException nfe){
            System.err.println(nfe.getMessage());            
        }
        return n;
    }
}