Boudreaux reached over and shook awake Thibodeaux, who had dozed off somewhere in New Mexico. "Where we at?" Thibodeaux groggily yawned.

"Not in Vegas, I gua-ran-tee, but could you get my knapsack?" Boudreaux asked, gesturing to the worn, leather backpack in the back seat of their cherry red Ford Miata.

"Why, is there a problem?"

"Just hand me my knapsack, problem or not."

Thibodeaux complied, glancing up as Boudreaux slowed the car to a stop in a line of vehicles approaching a toll booth. "$1.65 -- Exact change only," Thibodeaux read the yellow sign on the front of a small wooden building occupied by a lone toll booth operator. "I have to get $1.65 in exact change?" Thibodeaux asked, digging through the knapsack, "all I have are ten quarters, four dimes, and three pennies. I don't have any nickels . . ."

"Just give me five of the quarters and the four dimes," Boudreaux replied, holding out his hand.

"Oh yeah," Thibodeaux said, handing over the coins, "that does add up to $1.65. I wish there were an easy way to figure out if you have an exact monetary amount, given a set of coins."

"Hmmm," Boudreaux shrugged, "sounds like a good programming problem."