Greg has a pad. The pad's screen is an n × m rectangle, each cell can be either black or white. We'll consider the pad rows to be numbered with integers from 1 to n from top to bottom. Similarly, the pad's columns are numbered with integers from 1 to m from left to right.

Greg thinks that the pad's screen displays a cave if the following conditions hold:

  * There is a segment [l, r] (1 ≤ l ≤ r ≤ n), such that each of the rows l, l + 1, ..., r has exactly two black cells and all other rows have only white cells. 
  * There is a row number t (l ≤ t ≤ r), such that for all pairs of rows with numbers i and j (l ≤ i ≤ j ≤ t) the set of columns between the black cells in row i (with the columns where is these black cells) is the subset of the set of columns between the black cells in row j (with the columns where is these black cells). Similarly, for all pairs of rows with numbers i and j (t ≤ i ≤ j ≤ r) the set of columns between the black cells in row j (with the columns where is these black cells) is the subset of the set of columns between the black cells in row i (with the columns where is these black cells). 



Greg wondered, how many ways there are to paint a cave on his pad. Two ways can be considered distinct if there is a cell that has distinct colors on the two pictures.

Help Greg.

Input

The first line contains two integers n, m — the pad's screen size (1 ≤ n, m ≤ 2000).

Output

In the single line print the remainder after dividing the answer to the problem by 1000000007 (109 + 7).

Examples

Input

1 1


Output

0


Input

4 4


Output

485


Input

3 5


Output

451
#include <bits/stdc++.h>
using namespace std;
template <class T>
T By(T x, T y, T P) {
  T F1 = 0;
  while (y) {
    if (y & 1) {
      F1 += x;
      if (F1 < 0 || F1 >= P) F1 -= P;
    }
    x <<= 1;
    if (x < 0 || x >= P) x -= P;
    y >>= 1;
  }
  return F1;
}
template <class T>
T Mul(T x, T y, T P) {
  T F1 = 1;
  x %= P;
  while (y) {
    if (y & 1) {
      F1 = By(F1, x, P);
    }
    x = By(x, x, P);
    y >>= 1;
  }
  return F1;
}
template <class T>
T Gcd(T x, T y) {
  if (y == 0) return x;
  T z;
  while (z = x % y) {
    x = y, y = z;
  }
  return y;
}
template <class T>
void UpdateMin(T &x, T y) {
  if (y < x) {
    x = y;
  }
}
template <class T>
void UpdateMax(T &x, T y) {
  if (x < y) {
    x = y;
  }
}
template <class T>
T Sqr(const T x) {
  return x * x;
}
template <class T>
T Abs(const T x) {
  return x < 0 ? -x : x;
}
class ReadBuffer {
 private:
  char buff[20000000];
  char *buf;

 public:
  void init(int size = 20000000) {
    fread(buff, 1, size, stdin);
    buf = buff;
  }
  template <class T>
  bool readInteger(T &x) {
    x = 0;
    while (*buf && isspace(*buf)) ++buf;
    if (*buf == 0) return false;
    static bool flag;
    flag = 0;
    if (*buf == '-')
      flag = true;
    else
      x = *buf - '0';
    while (isdigit(*++buf)) x = x * 10 + *buf - '0';
    if (flag) x = -x;
    return true;
  }
  template <class T>
  bool readFloat(T &x) {
    long double nowpos = 0.1;
    x = 0;
    while (*buf && isspace(*buf)) ++buf;
    if (*buf == 0) return false;
    static bool flag, decimal;
    decimal = flag = 0;
    if (*buf == '-')
      flag = true, ++buf;
    else if (*buf == '.')
      decimal = true;
    while (isdigit(*buf) || *buf == '.') {
      if (*buf == '.')
        decimal = true;
      else {
        if (decimal) {
          x += nowpos * (*buf - '0');
          nowpos *= 0.1;
        } else {
          x = x * 10 + *buf - '0';
        }
      }
      ++buf;
    }
    return true;
  }
  bool readChar(char c) {
    if (*buf == 0) return 0;
    return c = *buf++, 1;
  }
  bool readString(char *s) {
    while (*buf && isspace(*buf)) ++buf;
    if (!*buf) return false;
    while (!isspace(*buf)) *s++ = *buf++;
    *s++ = 0;
    return true;
  }
  int countSpacetonext() {
    int total = 0;
    while (*buf && *buf == ' ') ++total, ++buf;
    return total;
  }
  bool splitBycharactor(char *s, char Split = '\n') {
    while (*buf && *buf != Split) *s++ = *buf++;
    *s++ = 0;
    return *buf != 0;
  }
};
long long dp[2011][2011];
const int MOD = 1000000007;
int n, m;
long long f[2011][2011];
long long g[2011][2011];
long long ff[2011];
int main() {
  for (int i = 1; i <= (2000); ++i) {
    int sum = 0;
    for (int j = 1; j <= (2000); ++j) {
      if (i == 1)
        dp[i][j] = j >= 2, g[i][j] = 1;
      else {
        g[i][j] = dp[i][j - 1] + sum;
        if (g[i][j] >= MOD) g[i][j] %= MOD;
        sum += dp[i - 1][j];
        if (sum >= MOD) sum -= MOD;
        dp[i][j] = dp[i][j - 1] + sum;
        if (dp[i][j] >= MOD) dp[i][j] -= MOD;
      }
    }
  }
  cin >> n >> m;
  for (int i = 1; i <= (n); ++i) {
    for (int j = 1; j <= (m); ++j) {
      ff[j] += dp[i][j];
      if (ff[j] >= MOD) ff[j] -= MOD;
      f[i][j] = f[i - 1][j] + ff[j];
      if (f[i][j] >= MOD) f[i][j] %= MOD;
    }
  }
  long long ans = 0;
  for (int i = 1; i <= (n); ++i) {
    for (int j = 1; j <= (m); ++j) {
      long long fff = g[i][j] * f[n + 1 - i][j];
      if (fff >= MOD) fff %= MOD;
      ans += fff * (m + 1 - j);
      if (ans >= MOD) ans %= MOD;
    }
  }
  cout << ans << endl;
  return 0;
}
