Time limit per test: 0.75 second(s) Memory limit: 65536 kilobytes
input: standard output: standard
There is only one elevator in the tall building with N floors. The parking for this building is at the basement floor which is located under the first floor. All floors are enumerated from 1 to N, growing up. At i-th floor there are Ai people who wish to descend from the floor to parking. You know that the elevator is unable to carry more than C people at any time. Descending or ascending one floor takes P seconds. Your task is to find the maximum possible number of people the elevator may deliver to parking within T seconds of operation, if it is located at the parking in the beginning. You may assume that stopping at a stage to load or unload people is done instantly.
In the first line of input file there are four integers N, C, P, T (1 ≤ N ≤ 100, 1 ≤ C ≤ 109, 1 ≤ P ≤ 109, 1 ≤ T ≤ 109). The second line contains the sequence of N integers A1, A2,..., AN (0 ≤ Ai ≤ 109). The sum of all Ai does not exceed 109 too.
Output the maximum possible number of people who can reach the parking.
4 5 2 15
0 1 2 3
4 5 2 18
0 1 2 3
3 2 1 9
1 1 1
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