a, b = map(int,input().split())
num = int(input())
time = list(map(int,input().split()))
time_num = a + b
total = []
for i in range(num):
    figure = time[i] % time_num
    figure -= a
    if figure > 0:
        count = b - figure
    elif figure == 0:
        count = b
    else:
        count = 0
    total.append(count)
end = 0
for i in range(num):
    end += total[i]
print(end)