import java.util.*;

//计算n到m的和

public class Main {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

System.out.println("请输入n,m(n<m)");

int n = scanner.nextInt();//输入起始值 较小值

int m = scanner.nextInt();//输入终值 较大值

int sum = 0;

while (n<=m) {

sum=sum+n;

n++;

}

System.out.print(sum);

}

}