import java.util.Scanner;
public class Leijia2{
	public static void main(String[] args){
		int sum = 0;
		Scanner in = new Scanner(System.in);
		System.out.print("计算从m到n的和\n");
		System.out.print("请输入m的值\n");
		int m = in.nextInt();
		System.out.print("请输入n的值\n");
		int n = in.nextInt();
		do
		{
			sum = sum + m;
			m++;
			
		}while(m<n);
		
		System.out.println(sum); 	
	}
	
}