from math import ceil
N,K,X,Y = map(int,input().split())
A = list(map(int,input().split()))
A.sort()
ans = 0
judge = Y // X
if judge < N:
    ans = ceil((A[N - judge - 1] - 1) / K) * Y
    #print(ans)
    c = ceil((A[N - judge - 1] - 1) / K)
    for j in range(N - judge, N):
        #print(ceil((A[j] - 1 - c * K) / K))
        ans += ceil((A[j] - 1 - c * K) / K)  * X
    print(ans)
else:
    for i in range(N):
        ans += ceil((A[i] - 1)/K) * X
    print(ans)