Do you want some lemons???
When he reaches the garden, he sees that there was a path which had 3 persons guarding 3 entrances.
He reaches the first guard, who says, "I will only allow you if you give me one more than half of whatever number of lemons you bring,"
John agrees, the second and third guard present the same condition. John agrees to all.
Now, the question, How many lemons did our little John bring so that he can satisfy all the three guards and save one for himself.