answer will be 65 for the 2nd test case?
input 3.
1 , 2 , 4 , 8. and b = 3
fill 1 litre on day 1 and 3 on day 2 , total cost = 7.
my greedy approach of taking as much as we can in a given range with minimum cost fails.
my idea for input 3, fill 3 on day 1, and 1 on day 4 but it gives a cost of 11 which is not optimal.