#include <iostream>
#include <vector>
using namespace std;
typedef long long ll;

int main(){
    ll H,W;
    cin >> H >> W;
    if(H==0){
        cout << 0 << endl;
        return 0;
    }
    cout << (H+1)*(2*W-H)/2 + max(H-W+1,0LL) << endl;
}