int main()
{
	int n,a[10],b[10],i,j,m=0;
	double GPA,c[10],d[10],l=0;
	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%d\n",&a[i]);
			}
	for(i=0;i<n;i++){
		scanf("%d",&b[i]);
	}
	for(i=0;i<n;i++){
		if((b[i]>=90)&&(b[i]<=100)){
			c[i]=4.0;
		}


	if((b[i]>=85)&&(b[i]<=89)){
			c[i]=3.7;
		}
	if((b[i]>=82)&&(b[i]<=84)){
			c[i]=3.3;
		}
	if((b[i]>=78)&&(b[i]<=81)){
			c[i]=3.0;
		}

	if((b[i]>=75)&&(b[i]<=77)){
			c[i]=2.7;
		}
	if((b[i]>=72)&&(b[i]<=74)){
			c[i]=2.3;
		}
	if((b[i]>=68)&&(b[i]<=71)){
			c[i]=2.0;
		}
	if((b[i]>=64)&&(b[i]<=67)){
			c[i]=1.5;
		}
	if((b[i]>=60)&&(b[i]<=63)){
			c[i]=1.0;
		}
	if(b[i]<60){
			c[i]=0;
		}
	}
	for(i=0;i<n;i++){
		d[i]=c[i]*a[i];
	}
	for(i=0;i<n;i++){
		l=l+d[i];
	}
	for(j=0;j<n;j++){
		m=m+a[j];
	}
	GPA=l/(double)m;
	printf("%.2lf\n",GPA);
	return 0;
}


	
