Consider the problem of a chain < A1, A2, A3, A4> of four matrices. Suppose that the dimensions of the matrices A1, A2, A3 and A4 are 30 × 35, 35 × 15, 15 × 5 and 5 × 10 respectively. The minimum number of scalar multiplications needed to compute the
product A1A2A3A4 is ____.