import bisect
import sys
import itertools
input=sys.stdin.readline

def main(args):
    N, K, X, Y = map(int,input().split())
    A = list(map(lambda x:-(-(int(x)-1)//K), input().split()))
    
    A.sort()
    
    if Y <= X:
        print(A[-1])
    else:
        ans = float('inf')
        cumsum = list(itertools.accumulate(A))
        cumsum = [0] + cumsum
        for i in range(N):#A[i]：ベホマラーの回数
            behoimi = cumsum[-1] - cumsum[i+1] - (N-(i+1))*A[i]
            mp = A[i]*Y + behoimi*X
            ans = min(ans, mp)
            
        ans = min(ans, cumsum[-1]*X)
        print(ans)

if __name__ == '__main__':
    main(sys.argv[1:])