#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;

int n,m;
int sum(int l, int r)
{
    int cnt=0;
    for (int i = l; i <=r; i ++ )
    {
        cnt+=i;
    }
    return cnt;
}

int main()
{
    cin >>n>>m;
    cout<<sum(n,m);


    return 0;

}