Numerical Methods: Euler to Runge–Kutta · Medium problem

A fossil's carbon-14 fraction remaining follows $y' = -\lambda y$ with $\lambda = \dfrac{\ln 2}{5730}$ per year (half-life $5730$ years), $y(0) = 1$. A simplified model takes one Euler step of size $h = 1000$ years to estimate the fraction remaining after $1000$ years. By how much does the true value $e^{-1000\lambda}$ exceed this Euler estimate? Round to the nearest thousandth.