A Tteokfire stays young by eating tteokguk, the Korean rice cake soup.
A Tteokfire ages one year for every bowl of tteokguk it eats. Digestion is instant, so it can eat as many bowls in one day as it likes. In exchange, a Tteokfire that goes a single day without tteokguk dies that day, no matter how much it ate before.
Didi knows only that one Tteokfire died on day M at age N. Didi wants to count how many ways that Tteokfire could have aged, but the count grows out of hand as the age rises, so counting by hand is hopeless.
A Tteokfire starts at age 0. One way of aging is the list of bowl counts for day 1 through day M in order, and two ways are different when the count differs on at least one day. The Tteokfire ate nothing on day M, which is why it died that day.
For N equal to 3 and M equal to 3 there are two ways: 1 bowl on day 1, 2 bowls on day 2 and 0 bowls on day 3, or 2 bowls on day 1, 1 bowl on day 2 and 0 bowls on day 3.