
int main()
{
	int n;
	scanf("%d", &n);
	int numble[10];
	int i,a;
    int s=0;
    double b;
    double sum=0;
    float GPA;
	for(i=0; i < n; i++){
		scanf("%d", &numble[i]);
        s = s + numble[i];
	}
		for(i=0; i < n; i++){
			scanf("%d", &a);
			if(a <= 100 && a >= 90){
               b = 4.0;
			}
			   else if(a <= 89 && a >=85){
				   b = 3.7;
			   }
				   else if(a <= 84 && a >= 82){
					   b = 3.3;
				   }
					   else if(a <= 81 && a >=78){
						   b = 3.0;
					   }
						   else if(a <= 77 && a >=75){
							   b = 2.7;
						   }
							   else if(a <= 74 && a >= 72){
								   b = 2.3;
							   }
								   else if(a <= 71 && a >= 68){
									   b = 2.0;
								   }
									   else if(a <= 67 && a >= 64){
									       b = 1.5;
									   }
									      else if(a <= 63 && a >= 60){
										   b = 1.0;
										  }
										     else if(a < 60){
											   b = 0;
											 }
										  
			sum = sum + numble[i] * b;
		}
	GPA =(float)( sum / s);
	printf("%.2f",GPA);
	return 0;
}


