#include <iomanip>
#include <iostream>
#include <functional>
#include <algorithm>
#include <math.h>
#include <cmath>
#include <string>
#include <vector>
#include<set>
#include<map>
#include <time.h>
typedef long long ll;

using namespace std;
int solve(int a){
	return a*a - ((a + 1)*a) / 2;
}
int factor(int x){
	if (x == 0)return 1;
	else return x*factor(x - 1);
}
int main(){
	int a, b;
	cin >> a >> b;
	b = min(a / 2, b);
	int ans = 0;
	ans += solve(2 * b);
	ans += 2*b*(a - 2 * b);
	cout << ans;
}