int main()
   {
          
          int j,k,n,l,sum;float GPA,bb;
          int b[10]={0},a[10]={0}; float c[10]={0};
          
        
          scanf("%d",&n);
         
           for(j=0;j<n;j++)
           {
               scanf("%d",&b[j]);          }
               
                sum=0;
                for(l=0;l<n;l++){
               
               sum+=b[l];
               //printf("%d\n",sum);
               }
               
               
               
            for(k=0;k<n;k++){
               scanf("%d",&a[k]); 
               if(a[k]<60)
                   c[k]=0;
               else if(a[k]<=63)
               c[k]=1.0 ;
               else if(a[k]<=67)
               c[k]=1.5;
               else if(a[k]<=71)
               c[k]=2.0;
               else if(a[k]<=74)
               c[k]=2.3;
               else if(a[k]<=77)
               c[k]=2.7;
               else if(a[k]<=81)
                c[k]=3.0;
                else if(a[k]<=84)
                c[k]=3.3;
               else if(a[k]<=89)
               c[k]=3.7;
                else if(a[k]<=100)
               c[k]=4.0;
                 }  
             
               for(l=0;l<n;l++)
               bb=b[l]*c[l]+bb;
               
               //printf("%d\n",sum);
               //printf("%f\n",bb);
               
               GPA=bb/sum;
                  printf("%.2f",GPA); 
                  //scanf("%d",&n);     
              

              return 0;
          
          }