Calculate the number 4020

It was mailman George's last day on the job after 35 years of delivering the mail through all kinds of weather. When he arrived at the first house on his route, the whole family came out, roundly congratulated him, and sent him on his way with a tidy gift envelope.
At the second house they presented him with a box of fine cigars. The folks at the third house handed him a selection of terrific fishing lures.
At the next house, he was met at the door by a strikingly beautiful woman in a revealing negligee. She took him by the hand, and led him up the stairs to the bedroom where she blew his mind with the most passionate love he had ever experienced.
When he'd had enough, they went downstairs, where she fixed him a giant breakfast: eggs, potatoes, ham, sausage, blueberry waffles and fresh-squeezed orange juice. When he was truly satisfied, she poured him a cup of steaming coffee. As she was pouring, he noticed a dollar bill sticking out from under the cup's bottom edge.
"All this is just too wonderful for words," he said, "but what's the dollar for?"
"Well," she said, "last night, I told my husband that today would be your last day, and that I wanted to do something special for you. I asked him what to give you. He said, 'Screw him. Give him a dollar.'"
"Breakfast was my idea."