#include<stdio.h>

int n;
double p[1001];
double q[1001];
int main(void) {
  int i;
  scanf("%d",&n);
  for( i = 0; i < n; i++ ) {
    int x;
    scanf("%d",&x);
    p[i] = x / 1000.0;
  }
  for( i = 0; i < n; i++ ) {
    int x;
    scanf("%d",&x);
    q[i] = x / 100.0;
  }
  for( i = 0; i < n; i++ )
    p[i] *= q[i];
  double exp = 0;
  double rem = 1.0;
  int c = 1;
  while(1) {
    double mp = p[0];
    int mi = 0;
    for( i = 1; i < n; i++ ) {
      if( mp < p[i] ) {
        mi = i;
        mp = p[i];
      }
    }
    exp += c * mp;
    rem -= mp;
    c++;
    if( rem * (c + exp) < exp * 1e-3 ) {
      exp = exp + rem * (c + exp);
      break;
    }
    p[mi] *= 1 - q[mi];
  }
  printf("%5f\n",exp);
  return 0;
}