a,b,c,d,e=map(int,input().split())
ame=a*(b-c)
kane=0
i=1
nedan=d
for _ in range(ame):
    if i%10 != 0:
        kane=kane+nedan
    elif nedan >= e:
        nedan=nedan-e
        kane=kane+nedan
    else:
        kane=kane+nedan
    i=i+1
print(kane)