By Manuel Garcia (should all be on one line):

print (lambda p:p[0]+'.'+p[1:])(str((lambda(x,y,t,a):2L*x*x//a)((lambda F:(lambda S:reduce(lambda(x,y,t,a), _:((x+y)//2L,S((x*y)//F),2L*t, (a-(t*(((x+y)//2L)**2-(S((x*y)//F))**2))//F)), [0]*13,(F, (F*F)//S(2L*F), 2L, F//2L)))(lambda n:reduce(lambda x, _:(x-x//2L+(n*F)//(2L*x)), [0]*15,n//2L)))(10L**(5010))))[:5000])


This slowly calculates and then outputs an estimate of pi to 5000 decimal places.

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