During the end blow period in LD steelmaking, the de-carburisation rate is expressed by the equation : dc/dt= -(c-c*) are the instantaneous and equilibrium concentration of carbon in steel respectively, in units of wt%. Given that c*= 0.04 wt % and c(t=0 min) =0.4 wt%, the concentration of carbon in steel (in wt%) at t=1 min is ______ (answer up to three decimal places)