I have two sorted vectors `x` and `y`. For each `y(i)`, I want to find the first index `j` such that `y(i) >= x(j)`.

Example:

```
x = [1 3 5 7 9 11 13 15]
y = [3 4 5 9 10 11]
result = [2 2 3 5 5 6]

```

What is the most efficient way to do that?