n = raw_input()
d = 1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991
ans = d * int(n)
s = str(ans)
#print ans
t = int(n)
if t <= 8:
	ss = "0." + s
	print ss
elif 9 <= t and t <= 81:
	ss = s[0] + '.' + s[1: len(s) - 1]
	print ss
else:
	ss = s[0] + s[1] + '.' + s[2:len(s) - 2]
	print ss