#include<bits/stdc++.h>
using namespace std;

#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

#define mygc(c) (c)=getchar_unlocked()
#define mypc(c) putchar_unlocked(c)

void reader(int *x){int k,m=0;*x=0;for(;;){mygc(k);if(k=='-'){m=1;break;}if('0'<=k&&k<='9'){*x=k-'0';break;}}for(;;){mygc(k);if(k<'0'||k>'9')break;*x=(*x)*10+k-'0';}if(m)(*x)=-(*x);}
void writer(double x, char c){printf("%.15f",x);mypc(c);}
template<class T> void writerLn(T x){writer(x,'\n');}

template <class T>
struct heapEx {
  int *hp, *place, size; T *val;

  void malloc(int N){hp=(int*)std::malloc(N*sizeof(int));place=(int*)std::malloc(N*sizeof(int));val=(T*)std::malloc(N*sizeof(T));}
  void free(){free(hp);free(place);free(val);}
  void* malloc(int N, void *workMemory){hp=(int*)workMemory;workMemory=(void*)(hp+N);place=(int*)workMemory;workMemory=(void*)(place+N);val=(T*)workMemory;workMemory=(void*)(val+N);return workMemory;}
  void init(int N){int i;size=0;rep(i,N)place[i]=-1;}
  void up(int n){int m;while(n){m=(n-1)/2;if(val[hp[m]]<=val[hp[n]])break;swap(hp[m],hp[n]);swap(place[hp[m]],place[hp[n]]);n=m;}}
  void down(int n){int m;for(;;){m=2*n+1;if(m>=size)break;if(m+1<size&&val[hp[m]]>val[hp[m+1]])m++;if(val[hp[m]]>=val[hp[n]])break;swap(hp[m],hp[n]);swap(place[hp[m]],place[hp[n]]);n=m;}}
  void change(int n, T v){T f=val[n];val[n]=v;if(place[n]==-1){place[n] = size;hp[size++] = n;up(place[n]);}else{if(f < v) down(place[n]); else if(f > v) up(place[n]);}}
  int pop(void){int res=hp[0];place[res]=-1;size--;if(size)hp[0]=hp[size],place[hp[0]]=0,down(0);return res;}
};

int N, P[2000], Q[2000];
double p[2000], q[2000];

int main(){
  int i, j, k, loop;
  double res = 0, pp = 1;
  heapEx<double> hp;

  reader(&N);
  rep(i,N) reader(P+i);
  rep(i,N) reader(Q+i);

  rep(i,N) p[i] = P[i] / 1000.0;
  rep(i,N) q[i] = Q[i] / 100.0;

  hp.malloc(N);
  hp.init(N);
  rep(i,N) hp.change(i, -p[i]*q[i]);

  rep(loop,400000){
    i = hp.hp[0];
    res -= (loop+1) * hp.val[i];
    p[i] += hp.val[i];
    pp += hp.val[i];
    hp.change(i, -p[i]*q[i]);
  }
  res += (400000 + res/(1-pp) + pp*(40000+res)) * pp;
  writerLn(res);

  return 0;
}