require "bigdecimal"
x = BigDecimal("1", 1000)
epsi = BigDecimal("1E-1000", 1000)
half = BigDecimal("0.5", 1000)
while (delta = (1 - 2 * x**2) * x * half).abs > epsi do x += delta end
print (x * 2).to_s[2,1001]