import bisect
import sys
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()
    
    ans = float('inf')
    l = 0
    behomara = 0
    while True:
        if behomara >= A[l]:
            l = bisect.bisect_right(A,behomara)
        #回復したい人数
        res = N - l
        if Y < res*X:
            behomara += 1
        else:
            behoimi = sum(map(lambda x:x-behomara,A[l:]))
            break
        if res == 0:
            break
            
    print(X*behoimi+Y*behomara)

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