n, d = list(map(int, input().split()))
a = list(map(int, input().split()))
m = int(input())
a.sort()
if m <= n:
print(sum(a[:m]))
else:
print((sum(a) + (n - m) * d))
1288A - Deadline | 1617A - Forbidden Subsequence |
914A - Perfect Squares | 873D - Merge Sort |
1251A - Broken Keyboard | 463B - Caisa and Pylons |
584A - Olesya and Rodion | 799A - Carrot Cakes |
1569B - Chess Tournament | 1047B - Cover Points |
1381B - Unmerge | 1256A - Payment Without Change |
908B - New Year and Buggy Bot | 979A - Pizza Pizza Pizza |
731A - Night at the Museum | 742A - Arpa’s hard exam and Mehrdad’s naive cheat |
1492A - Three swimmers | 1360E - Polygon |
1517D - Explorer Space | 1230B - Ania and Minimizing |
1201A - Important Exam | 676A - Nicholas and Permutation |
431A - Black Square | 474B - Worms |
987B - High School Become Human | 1223A - CME |
1658B - Marin and Anti-coprime Permutation | 14B - Young Photographer |
143A - Help Vasilisa the Wise 2 | 320A - Magic Numbers |