best excercise for burning fat ??

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Hi everyone, im currently on a mission of losing 5 stone and wondered if anyone could give me some tips on exercise, i trying the couch to 5k at the moment but because i am very large im finding it hard to even do the first week ! my calfs and shins burn and go numb but i am trying every day.

I have wedding to attend in august and need to get most of the weight off by then ! i know its a big task any help would be greatly appretiated

hayley x x x