def legoBlocks(n, m):
    f = [1]
    g = [1]
    h = [1]
    for i in range(1, m + 1):
        sumhg = 0
        for j in range(1, i):
            sumhg += h[j] * g[i-j] % (10**9+7)
        f.append(sum(f[-4:]) % (10**9+7))    
        g.append(f[i] ** n % (10**9+7))
        h.append((g[i] - sumhg) % (10**9+7))
    return h[-1] % (10**9+7)