So it will be difficult to do this, but here it goes:

0 - m/e (((x sub(k+1) - x sub(k))/e - ((x sub(k) - x sub(k-1))/e) - V(x)

0 : average values of action S are zero

m: mass

e: small difference between successive times t1, t2, t3... In other words, t sub(i + 1) - t sub (i) = e where the limit is Planck's constant

x sub(k+1) - x sub(k))/e : velocity

(see: "The Beat of a Different Drum: The life and science of Richard Feynman", Ed Regis, Reprinted 1996, p.189 equation 10.5).

Warm regards, Harv