int main(){
	int a[1000],n,i,b[1000];
	double c[1000],e,x=0,y=0,z;
	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%d",&a[i]);
	}
	for(i=0;i<n;i++){
		scanf("%d",&b[i]);
	}
	for(i=0;i<n;i++){
		c[i]=0;
	}
	for(i=0;i<n;i++){
		if(b[i]>=90){
			c[i]=4.0;
		}else{
			if(b[i]<90&&b[i]>=85){
				c[i]=3.7;
			}else{
				if(b[i]<85&&b[i]>=82){
					c[i]=3.3;
				}else{
					if(b[i]<82&&b[i]>=78){
						c[i]=3.0;
					}else{
						if(b[i]<78&&b[i]>=75){
							c[i]=2.7;
						}else{
							if(b[i]<75&&b[i]>=72){
								c[i]=2.3;
							}else{
								if(b[i]<72&&b[i]>=68){
									c[i]=2.0;
								}else{
									if(b[i]<68&&b[i]>=64){
										c[i]=1.5;
									}else{
										if(b[i]<64&&b[i]>=60){
											c[i]=1.0;
										}else{
											if(b[i]<60){
												c[i]=0;
											}
										}
									}
								}
							}
						}
					}
				}
			}
		}
	}
	for(i=0;i<n;i++){
		e=c[i]*a[i];
		x+=e;
		y+=a[i];
	}
	z=x/y;
	printf("%.2lf\n",z);
    return 0;
}