#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;
    }
    ll N = min(W-1,H);
    cout << W*N - N*(N+1)/2 + N + max(H-W+1,0LL) << endl;
}