An addition chain of a given number K is an increasing sequence of integers that start with 1 and end with K. Furthermore, each member of the sequence, except the first, is the sum of two (not necessarily distinct) members. For example, (1, 2, 3, 4) is an addition chain of 4. The problem is given a number 1 <= N <= 300, what is the minimal length of the addition chain of N?