If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

始めの問題だけあって簡単。手計算でできる。 

p001 = sum [n|n<-[1..999],mod n 3 ==||mod n 5==]