#include <iostream>
using namespace std;
int n, k, catul, restul, suma, nr;
int main()
{
cout << "n= "; cin >> n;
cout << "k= "; cin >> k;
catul=n/k;
restul=n%k;
nr=k-1;
if (nr%2==0) suma=catul*(nr/2)*(1+nr);
else suma=catul*nr*(1+nr)/2;
if (restul%2==0) suma=suma+(1+restul)*restul/2;
else suma=suma+restul*(restul+1)/2;
cout << suma;
}
