Suppose there are two kinds of balls (i.e. Good ball and Bad ball) in a bag. Now I take out all the balls one by one and put them in a line. We denote Good ball as 1 and Bad ball as 0. If there are total n balls, then the line can be represented as a vector of size n, where a_i is denoted as follows,

Now I want to define a evaluation method M to measure . My idea is that the earlier we select out Good balls, the higher value of M. Thus should get the highest M.

Up to now, we want to define M to meet following conditions,

1. Different has different M
2. The earlier good balls are found, the higher value of M should be.