include [HTML_REMOVED]
include [HTML_REMOVED]
include [HTML_REMOVED]
using namespace std;
int sum(int l, int r){
long long s=0;
for(int i=l;i<=r;i++){
s+=i;
}
return s;
}
int main()
{
int l,r;
cin>>l>>r;
cout<<sum(l,r);
return 0;
}