In a very long toy train, the first and last cars were blue. After each blue car (except the last one), there were two yellow cars. After
each pair of yellow cars, there was a red car. After each red car,
there was a blue car. The first five train cars are shown in the
picture. Oleg picked a car and recolored all cars in front of it green.
Then Joyce picked a car and recolored all cars behind it green.
What is the least possible number of non-green cars in the
recolored toy train if it contains 7 more yellow cars than blue cars?