Which is the one leg left without being cut by the Kalipurusha?

Sathyam (truth),  Dharmam ( right way of living), Dhaanam (Charity), Shaucham (Purity) are the 4 legs of the cow, which was the seen by Raja Pareekshith at the time of start of Kaliyuga. 

And Three legs were already cut by the Kali purusha. The One leg left was sathyam, As in Bhagavatham.

  

There is an unseen coincidence here.

Indian flag has these 4 legs as colors and symbol.

Orange - Dhanam or thyaga in turn to sacrifice

White - Shaucham or purity in turn to cleanliness

Green - Dharmam or duty in turn to prosperity

Chakra - Sathyam or truth in turn the time

The only left is Sathyam means the truth. The ultimate truth is impermanence of our life in this world. If our mind stays on this truth of death, we become strong and unshakeable.    

Also Mahathma Gandhi used this as his main motive

(My experiments with the truth) 

Sathyameva Jayathe!

Truth only wins!

Let's teach the world the truth, that is (we breath) athmagyan which will save people from the sufferings given by the Kalipurusha.

http://www.artofliving.org/in-en/happiness-program