You pass a homeless man in America, who asks you for exactly one dollar. You pull out all the change in your pocket, and tell him that you can't help him since you dont have the exact amount of change to make a dollar.

Whats the largest amount of money that you could have had in your pocket?

Bonus Points for the smarty pants in /sci/: How can you generalize the solution if he asks you for N dollars, and the coins in the country you're in have value of a,b,c,d ... cents respectively