P3052 [USACO12MAR] Cows in a Skyscraper G

A little known fact about Bessie and friends is that they love stair climbing races. A better known fact is that cows really don't like going down stairs. So after the cows finish racing to the top of their favorite skyscraper, they had a problem. Refusing to climb back down using the stairs, the cows are forced to use the elevator in order to get back to the ground floor. The elevator has a maximum weight capacity of $W$ ($1

\* Line $1$: $N$ and $W$ separated by a space. \* Lines $2$ ~ $N+1$: Line $i+1$ contains the integer $C_i$, giving the weight of one of the cows.

\* A single integer, $R$, indicating the minimum number of elevator rides needed.

There are four cows weighing 5, 6, 3, and 7 pounds. The elevator has a maximum weight capacity of 10 pounds. We can put the cow weighing 3 on the same elevator as any other cow but the other three cows are too heavy to be combined. For the solution above, elevator ride 1 involves cow #1 and #3, elevator ride 2 involves cow #2, and elevator ride 3 involves cow #4. Several other solutions are possible for this input.