According to
http://www.the-perfectshape.com/tag/calories/
"It is very important to remember that the human fat tissue contains approximately 87% lipids. This means that 1 kg of body-fat tissue has the caloric energy of 870 g of pure fat, representing about 7,800 Kcal. So, in order to lose 1 kg of body fat, you have to create an energy deficit (consume more than assimilate) of 7,800 Kcal."
(consume = burn up , not eat)
If 7800 Kcal = 7800000 cal then… exercise exercise exercise
20 x 7800 Kcals all the best.