I have this matrix:

```
matrix = [[a,r],[b,r],[c,r],[c,t,n],[b,t,n],[b,a]]

```

I want to count how many times did "n" appear in the matrix, but there is a condition. If the first letter is next to an "a" or an "r", it doesn't count as "n" appeared.
For example, in this list "n" appeared one time, because we have to discount the second time it appeared, due to the fact that the letter "b" later appeared next to an "a".

I've tried this:

```
c = 0
for i in range(len(matrix)):
    if n in matrix[i]:
         c+=1

```

But I have failed in all the conditions that I've tried if the letter that is next to "n" appears again next to an "a"