Viagra for Grandpa

Grandpa and Grandma were living with their son and daughter-in-law. Grandpa noticed that his son had a bottle of Viagra and asked if he could have one. His son said, "Dad, I don't think you should take one, they're very strong and expensive." Grandpa said, "I know, but I want to try one. How much are they?" His son replied, "$30 each." Grandpa only had a $50 bill but was going to the bank. He told his son that he would leave $30 under his pillow that night. The next morning his son found $130 under his pillow and said, "Dad, I told you it was only $30. There's $130 under my pillow!" Grandpa said, "That's ok, the other $100 is from Grandma!"