How to make a function that counts how many times each element is equal to 2 elements to its right

Question

I know i need to use a list comprehension but for the life of me I cannot figure out what would be the correct way to denote this. An example of this running right would be for

Answer 1

s='evening'
print len([x for x,y in zip(s, s[2:]) if x==y])

Output:

2