import Math.Statistics.Fusion
import Data.Array.Vector
import Text.Printf
import Data.List

-- main = printf "%f\n" (mean (replicateU 1000000000 (pi :: Double)))

main = printf "%f\n" (mean (replicate 1000000000 (pi :: Double)))
    where
        mean x = fst $ foldl' (\(!m, !n) x -> (m+(x-m)/(n+1),n+1)) (0,0) x

{-

Main_zdwfold_info:
.Lc122:
  movq %rdi,%rax
  cmpq $10000000,%rax
  jne .Lc126
  movq %rsi,%rbx
  jmp *(%rbp)
.Lc126:
  incq %rax
  leaq 1(%rsi),%rcx
  cvtsi2sdq %rsi,%xmm0
  movsd .Ln128(%rip),%xmm7
  subsd %xmm5,%xmm7
  divsd %xmm0,%xmm7
  addsd %xmm7,%xmm5
  movq %rcx,%rsi
  movq %rax,%rdi
  jmp Main_zdwfold_info

-}