#include <fstream>
using namespace std;
typedef unsigned long long int ULLINT;

ULLINT sum(ULLINT ,ULLINT);

int main()
{
ifstream in("input.txt");
ofstream out("output.txt");

ULLINT N,K, rooms;
in >> N >> K;
rooms = 1 + (N-1) * K + sum(N,K);
out << rooms;
return 0;
}

ULLINT sum(ULLINT n ,ULLINT k)
{
    ULLINT siski = 0;
    for(int i=0; i < k; i++)
    {
        siski += (n-2) * i;
    }
    return siski;
}