#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); }