#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<queue>
#include<cmath>
#include<cstdio>
#include<tuple>
#include<bitset>
#include<map>

using namespace std;
#define int long long
#define rep(i,n) for(int i=0;i<n;++i)
#define rep1(i,n) for(int i=1;i<=n;++i)
#define ALL(x) x.begin(),x.end()
#define debug(output) cout<<#output<<"= "<<output<<endl

using P=pair<int,int>;
using lint=long long;
using ll=long long;
const lint inf=1e18+7;
const int MOD=1000000007;
signed main(){
  lint n,m,c;cin>>n>>m>>c;
  vector<lint> a(n),b(m);
  rep(i,n)cin>>a[i];
  rep(i,m)cin>>b[i];
  b.push_back(0);
  lint sm=0;
  sort(a.begin(),a.end());
  sort(b.begin(),b.end());
  b.push_back(c/a[0]+1+b[m]);
  int cur=m+1;
  rep(i,n){
    while(b[cur]*a[i]>c)--cur;
    sm+=m-cur;
  }
  double res=(double)sm/(double)n/(double)m;
  printf("%.12lf\n",res);
  return 0;
}