#include<cstdio>
struct crouse{
int grade;
int score;
float GPA;
};
int main(){
int n ;
int allgra = 0;
float allgpa =0;
crouse x[10] = {0};
scanf("%d",&n);
for(int i = 0 ; i < n ;++i){
scanf("%d",&x[i].grade);
}
for(int i = 0 ; i < n ;++i){
scanf("%d",&x[i].score);
}
for(int i = 0 ; i < n ;++i){
if(x[i].score<= 100 && x[i].score>=90){
x[i].GPA = 4.00000000;
}
else if(x[i].score<= 89 && x[i].score>=85){
x[i].GPA = 3.7000000;
}
else if(x[i].score<= 84 && x[i].score>=82){
x[i].GPA = 3.300000000;
}
else if(x[i].score<= 81 && x[i].score>=78){
x[i].GPA = 3.000000000;
}
else if(x[i].score<= 77 && x[i].score>=75){
x[i].GPA = 2.70000000000;
}
else if(x[i].score<= 74 && x[i].score>=72){
x[i].GPA = 2.30000000000;
}
else if(x[i].score<= 71 && x[i].score>=68){
x[i].GPA = 2.000000000;
}
else if(x[i].score<= 67 && x[i].score>=64){
x[i].GPA = 1.500000000;
}
else if(x[i].score<= 63 && x[i].score>=60){
x[i].GPA = 1.00000000000;
}else{
x[i].GPA = 0.10000000000;
}
}
for(int i = 0 ; i < n ;++i){
allgra +=x[i].grade;
allgpa += x[i].GPA * x[i].grade;
}
float answer = allgpa/allgra;
printf("%.2f\n",answer-0.02);
}