How to charge an iphone 4 with an iphone 5 charger?

How can i charge an iphone 4 with an iphone 5 charger?

You can't, the connector is not the same.

You can get a 30pin cable which is used by all devices iPhone 4s and below.
they sell for like $1-$2 on ebay

Can't.

You can buy an adapter. I know you can get one that turns the iPhone 4 charger into an iPhone 5 charger but I'm sure I saw a 5 to 4 one on eBay or Amazon.