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#include <bits/stdc++.h>


using namespace std;


const int MOD = 1000 * 1000 * 1000 + 7;


void add(int &x, int v) {
    x += v;
    if (x >= MOD) {
        x -= MOD;
    }
}

void addProd(int &x, int a, int b) {
    x = (x + (long long) a * b) % MOD;
}

int solve(int n, int m) {
    vector <vector<int>> dp(2, vector <int> (n + 1, 0));
    dp[1][0] = 1;

    for (int t = 0; t < n; t++) {
        vector <vector<int>> dpNew(2, vector <int> (n + 1, 0));
        for (int full = 0; full <= 1; full++) {
            for (int numOpen = 0; numOpen <= min(t, m); numOpen++) {
                addProd(dpNew[1][numOpen], numOpen, dp[full][numOpen]);

                if (numOpen < m) {
                    addProd(dpNew[0][numOpen + full], m - numOpen, dp[full][numOpen]);
                }
            }
        }

        dp = dpNew;
    }

    int ans = 0;
    for (int numOpen = 0; numOpen <= n; numOpen++) {
        add(ans, dp[1][numOpen]);
    }

    return ans;
}

int main() {
    ios_base::sync_with_stdio(false);

    int n, m;
    cin >> n >> m;

    cout << solve(n, m);

    return 0;
}