a,b,c,d,e=map(int,input().split())
n=a*(b-c)
if n==0:
    print(0);exit()
ans=d
now=d
for i in range(2,n+1):
    if i%10!=0:ans+=now
    else:
        if e<=now:
            now-=e
            ans+=now
        else:ans+=now
print(ans)