#45435: easy
0801elmer666@gmail.com
(薛冠志)
a, b = map(int,input().split())
num = int(input())
time = list(map(int,input().split()))
total = 0
for i in range(num):
total_num = 0
one = a + b
plus = time[i] % one
green = plus - a
if green < 0:
total_num = 0
elif green == 0:
total_num = b
else:
total_num = b - green
total += total_num
print(total)