We have N+1 integers: 10^{100}, 10^{100}+1, ..., 10^{100}+N.

We will choose K or more of these integers. Find the number of possible values of the sum of the chosen numbers, modulo (10^9+7).

Constraints

* 1 \leq N \leq 2\times 10^5
* 1 \leq K \leq N+1
* All values in input are integers.

Input

Input is given from Standard Input in the following format:


N K


Output

Print the number of possible values of the sum, modulo (10^9+7).

Examples

Input

3 2


Output

10


Input

200000 200001


Output

1


Input

141421 35623


Output

220280457
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Tarek
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        DSumOfLargeNumbers solver = new DSumOfLargeNumbers();
        solver.solve(1, in, out);
        out.close();
    }

    static class DSumOfLargeNumbers {
        final static int MOD = 1000000007;

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            int m = in.nextInt();
            long ans = 0, pre = 0, suf = 0;
            for (int i = 1; i <= n + 1; i++) {
                pre += i - 1;
                suf += n + 1 - i;
                pre %= MOD;
                suf %= MOD;
                if (i >= m) {
                    ans += suf - pre + 1 + MOD;
                    ans %= MOD;
                }
            }
            out.println(ans);
        }

    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

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

    }
}

