int main(){
int a[11],b[11],n,i,m=0;
float c[11],g,d=0;
scanf("%d",&n);
for (i=1;i<=n;i++)
scanf("%d",&a[i]);
for (i=1;i<=n;i++)
scanf("%d",&b[i]);
for (i=1;i<=n;i++)
{
if (b[i]<=100&&b[i]>=90)
c[i]=4.0;
if (b[i]<=89&&b[i]>=85)
c[i]=3.7;
if (b[i]<=84&&b[i]>=82)
c[i]=3.3;
if (b[i]<=81&&b[i]>=78)
c[i]=3.0;
if (b[i]<=77&&b[i]>=75)
c[i]=2.7;
if (b[i]<=74&&b[i]>=72)
c[i]=2.3;
if (b[i]<=71&&b[i]>=68)
c[i]=2.0;
if (b[i]<=67&&b[i]>=64)
c[i]=1.5;
if (b[i]<=63&&b[i]>=60)
c[i]=1.0;
if (b[i]<60)
c[i]=0.0;

}
for (i=1;i<=n;i++)
{
c[i]=c[i]*a[i];
}
for (i=1;i<=n;i++)
{
d=d+c[i];
m=m+a[i];
}
g=d/m;
printf("%.2f",g);

return 0;
}