A circular prime is a prime number which remains prime on any cyclic rotation of its digits. For example, 1193 is a circular prime, as 1931, 9311 and 3119 are also primes. 337 is another one. Write a function to find the number of circular primes less than any given number. (For example, there are 8 circular primes less than 40 (2, 3, 5, 7, 11, 13, 17, 37 - counting only the smallest in each circle)