n, k, x, y = map(int, input().split())
A = list(map(int, input().split()))

B = [0]*n
for i, a in enumerate(A):
    if (a-1)%k == 0:
        B[i] = (a-1)//k
    else:
        B[i] = (a-1)//k+1
B.sort()
#print(B)

import math
k = math.ceil(y/x)

if k == 0:
    ans = B[-1]*y
    print(ans)
    exit()

if k > n:
    ans = sum(B)*x
    print(ans)
    exit()

ans = y*B[n-k]
for i in range(n-k, n):
    b = B[i]-B[n-k]
    ans += x*b
print(ans)