CF237C Primes on Interval

You've decided to carry out a survey in the theory of prime numbers. Let us remind you that a prime number is a positive integer that has exactly two distinct positive integer divisors. Consider positive integers $ a $ , $ a+1 $ , $ ... $ , $ b $ $ (a

A single line contains three space-separated integers $ a,b,k $ ( $ 1

In a single line print a single integer — the required minimum $ l $ . If there's no solution, print -1.