#include <iostream>
using namespace std;
const int N = 1010;
int l,r;
int sum(int l,int r){
    int res = 0;
    for(int i = l;i <= r;++i)   res += i;
    return res;
}
int main(){
    cin >> l >> r;
    cout << sum(l,r) << endl;
    return 0;
}