Sasha is a very happy guy, that's why he is always on the move. There are n cities in the country where Sasha lives. They are all located on one straight line, and for convenience, they are numbered from 1 to n in increasing order. The distance between any two adjacent cities is equal to 1 kilometer. Since all roads in the country are directed, it's possible to reach the city y from the city x only if x < y. 

Once Sasha decided to go on a trip around the country and to visit all n cities. He will move with the help of his car, Cheetah-2677. The tank capacity of this model is v liters, and it spends exactly 1 liter of fuel for 1 kilometer of the way. At the beginning of the journey, the tank is empty. Sasha is located in the city with the number 1 and wants to get to the city with the number n. There is a gas station in each city. In the i-th city, the price of 1 liter of fuel is i dollars. It is obvious that at any moment of time, the tank can contain at most v liters of fuel.

Sasha doesn't like to waste money, that's why he wants to know what is the minimum amount of money is needed to finish the trip if he can buy fuel in any city he wants. Help him to figure it out!

Input

The first line contains two integers n and v (2 ≤ n ≤ 100, 1 ≤ v ≤ 100) — the number of cities in the country and the capacity of the tank.

Output

Print one integer — the minimum amount of money that is needed to finish the trip.

Examples

Input


4 2


Output


4


Input


7 6


Output


6

Note

In the first example, Sasha can buy 2 liters for 2 dollars (1 dollar per liter) in the first city, drive to the second city, spend 1 liter of fuel on it, then buy 1 liter for 2 dollars in the second city and then drive to the 4-th city. Therefore, the answer is 1+1+2=4.

In the second example, the capacity of the tank allows to fill the tank completely in the first city, and drive to the last city without stops in other cities.
import java.io.*;
import java.math.*;
import java.util.*;

public class test {

	public static void main(String[] args) {
//		int test = fs.nextInt();
		int test = 1;
		for (int cases = 0; cases < test; cases++) {
			int n = fs.nextInt();
			int v = fs.nextInt();
			if (n > v) {
				int cost = v;
				int filled = v;
				int pos = 1;
				while (v != (n - pos)) {
					++pos;
					cost += pos;
				}
				System.out.println(cost);
			}
			else
				System.out.println(n-1);
		}
	}

	/*
	 * array list
	 * 
	 * ArrayList<Integer> al=new ArrayList<>(); creating BigIntegers
	 * 
	 * BigInteger a=new BigInteger(); BigInteger b=new BigInteger();
	 * 
	 * hash map
	 * 
	 * HashMap<Integer,Integer> hm=new HashMap<Integer,Integer>(); for(int
	 * i=0;i<ar.length;i++) { Integer c=hm.get(ar[i]); if(hm.get(ar[i])==null) {
	 * hm.put(ar[i],1); } else { hm.put(ar[i],++c); } }
	 * 
	 * while loop
	 * 
	 * int t=sc.nextInt(); while(t>0) { t--; }
	 * 
	 * array input
	 * 
	 * int n = sc.nextInt(); int ar[] = new int[n]; for (int i = 0; i < ar.length;
	 * i++) { ar[i] = sc.nextInt(); }
	 */
	static class Graph {
		HashMap<Character, LinkedList<Character>> hm = new HashMap<Character, LinkedList<Character>>();

		private void addVertex(char vertex) {
			hm.put(vertex, new LinkedList<>());
		}

		private void addEdge(char source, char dest, boolean bi) {
			if (!hm.containsKey(source))
				addVertex(source);
			if (!hm.containsKey(dest))
				addVertex(dest);
			hm.get(source).add(dest);
			if (bi) {
				hm.get(dest).add(source);
			}
		}

		private boolean isCyclicUtil(char ch, boolean visited[], char parent, HashMap<Character, Integer> index) {
			visited[index.get(ch)] = true;
			Iterator<Character> it = hm.get(ch).iterator();
			while (it.hasNext()) {
				Character character = (Character) it.next();
				if (!visited[index.get(character)]) {
					if (isCyclicUtil(character, visited, ch, index))
						return true;
				} else if (character != ch)
					return true;
			}
			return false;
		}

		private boolean isCyclic(HashMap<Character, Integer> index) {
			boolean visited[] = new boolean[hm.size()];
			Set<Character> set = hm.keySet();
			for (Character character : set) {
				if (!visited[index.get(character)]) {
					if (isCyclicUtil(character, visited, '-', index))
						return true;
				}
			}
			return false;
		}
	}

	static class Node {
		Node left, right;
		int data;

		public Node(int data) {
			this.data = data;
		}

		public void insert(int val) {
			if (val <= data) {
				if (left == null) {
					left = new Node(val);
				} else {
					left.insert(val);
				}
			} else {
				if (right == null) {
					right = new Node(val);
				} else {
					right.insert(val);
				}
			}
		}

		public boolean contains(int val) {
			if (data == val) {
				return true;
			} else if (val < data) {
				if (left == null) {
					return false;
				} else {
					return left.contains(val);
				}
			} else {
				if (right == null) {
					return false;
				} else {
					return right.contains(val);
				}
			}
		}

		public void inorder() {
			if (left != null) {
				left.inorder();
			}
			System.out.print(data + " ");
			if (right != null) {
				right.inorder();
			}
		}

		public int maxDepth() {
			if (left == null)
				return 0;
			if (right == null)
				return 0;
			else {
				int ll = left.maxDepth();
				int rr = right.maxDepth();
				if (ll > rr)
					return (ll + 1);
				else
					return (rr + 1);
			}
		}

		public int countNodes() {
			if (left == null)
				return 1;
			if (right == null)
				return 1;
			else {
				return left.countNodes() + right.countNodes() + 1;
			}
		}

		public void preorder() {
			System.out.print(data + " ");
			if (left != null) {
				left.inorder();
			}

			if (right != null) {
				right.inorder();
			}

		}

		public void postorder() {
			if (left != null) {
				left.inorder();
			}

			if (right != null) {
				right.inorder();
			}
			System.out.print(data + " ");

		}

		public void levelorder(Node node) {
			LinkedList<Node> ll = new LinkedList<Node>();
			ll.add(node);
			getorder(ll);

		}

		public void getorder(LinkedList<Node> ll) {
			while (!ll.isEmpty()) {
				Node node = ll.poll();
				System.out.print(node.data + " ");
				if (node.left != null)
					ll.add(node.left);
				if (node.right != null)
					ll.add(node.right);
			}
		}
	}

	static class FastReader {
		BufferedReader br;
		StringTokenizer st;

		public FastReader() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}
	}

	static class Pair {
		int first, second;

		public Pair(int first, int second) {
			this.first = first;
			this.second = second;
		}

	}

	static class OutputWriter {
		private final PrintWriter writer;

		public OutputWriter(OutputStream outputStream) {
			writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
		}

		public OutputWriter(Writer writer) {
			this.writer = new PrintWriter(writer);
		}

		public void print(Object... objects) {
			for (int i = 0; i < objects.length; i++) {
				if (i != 0)
					writer.print(' ');
				writer.print(objects[i]);
			}
		}

		public void printLine(Object... objects) {
			print(objects);
			writer.println();
		}

		public void close() {
			writer.close();
		}

		public void flush() {
			writer.flush();
		}

	}

	private static final Scanner sc = new Scanner(System.in);
	private static final FastReader fs = new FastReader();
	private static final OutputWriter op = new OutputWriter(System.out);

	static int[] getintarray(int n) {
		int ar[] = new int[n];
		for (int i = 0; i < n; i++) {
			ar[i] = fs.nextInt();
		}
		return ar;
	}

	static long[] getlongarray(int n) {
		long ar[] = new long[n];
		for (int i = 0; i < n; i++) {
			ar[i] = fs.nextLong();
		}
		return ar;
	}

	static int[][] get2darray(int n, int m) {
		int ar[][] = new int[n][m];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				ar[i][j] = fs.nextInt();
			}
		}
		return ar;
	}

	static Pair[] getpairarray(int n) {
		Pair ar[] = new Pair[n];
		for (int i = 0; i < n; i++) {
			ar[i] = new Pair(fs.nextInt(), fs.nextInt());
		}
		return ar;
	}

	static void printarray(int ar[]) {
		for (int i : ar) {
			op.print(i + " ");
		}
		op.flush();
	}

	static int fact(int n) {
		int fact = 1;
		for (int i = 2; i <= n; i++) {
			fact *= i;
		}
		return fact;
	}

//	

	// function to find largest prime factor

}/*
	 * 1 5 -2 -3 -1 -4 -6till here
	 */

//		while (t > 0) {
//			int a[] = getintarray(3);
//			int b[] = getintarray(3);
//			int ans = getans(a, b);
//			System.out.println(ans);
//		}