import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
 
	public static double sumRange(double begin, double end) {
		return ((end - (begin-1)) * (end + begin) ) / 2;
	}
	public static void main (String[] args) throws java.lang.Exception
	{
		System.out.println(sumRange(1, 1000));
		System.out.println(sumRange(500, 1000));
		System.out.println(sumRange(20, 300));
	}
}

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