
int main(int argc, char* argv[])
{
   int i,n;
   int sz[10],sum=0;;
   double b[10];
   double c[10];
   double total=0;
   float GPA;
   0<n<10;
    scanf("%d",&n);
   for(i=0;i<n;i++){
     scanf("%d",&sz[i]);}
  for(i=0;i<n;i++){
     scanf("%lf",&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++){
		sum+=sz[i];
	}

	for(i=0;i<n;i++){
		total+=c[i]*sz[i];
	}

      GPA=total/sum;
   printf("%.2f",GPA);
return 0;
} 
