N,K,X,Y = map(int, input().split())
A = [int(a) for a in input().split()]

for i in range(N):
    if (A[i]-1)%K == 0:
        A[i] = (A[i]-1)//K
    else:
        A[i] = (A[i]-1)//K+1

A.sort()
ans = 0
import bisect
cnt = 0
idx = bisect.bisect_right(A, cnt)
while idx < N:
    if (N-idx)*X > Y:
        ans += Y*(A[idx]-cnt)
        cnt = A[idx]
        idx = bisect.bisect_right(A, cnt)
    else:
        for i in range(idx, N):
            ans += X*(A[i]-cnt)
        break

print(ans)