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