import java.io.;
import java.util.;

public class Main{
public static void main(String args[]) {
Scanner cin = new Scanner(System.in);

    var l = cin.nextInt();
    var r = cin.nextInt();

    System.out.println(sum(l, r));
}
public static int sum(int l, int r){
    int s = 0;
    for(int i = l; i <= r; i++){
        s += i;
    }
    return s;
}

}