main = interact $ unlines . map (show . chebyshev . read) . init . lines

chebyshev n = length $ takeWhile (<= 2*n) $ dropWhile (<= n) primes

primes = 2:3:[x | i<-[1..], j<-[-1,1], let x = 6*i+j, isPrime x]
 where isPrime n = null [i | i<-takeWhile (\x -> x*x <= n) primes, rem n i == 0]