program rk2
      
      implicit none

      real x,t,dt,f
      open(unit=13,file="data.d")

      dt = 0.125
      x = 1

      do 10 t=0,5,dt
         write(13,*) t,x
         x = x + 0.5*(f(x,t)+f(x+f(x,t)*dt,t+dt))*dt
 10   continue

      stop
      end

      real function f(x,t)
      real x,t
      f = -x**5 + cos(t**2)
      return
      end