#include<bits/stdc++.h>
using namespace std;
#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
#define vec vector<ll>
#define mat vector<vector<ll> >
#define fi first
#define se second
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
typedef long double ld;
typedef complex<double> comp;
const ll INF=1e9+7;
const ll inf=INF*INF;
const ll MOD=1e9+7;
const ll mod=MOD;
const int MAX=1000010;
const double PI=acos(-1.0);


signed main(){
    ll n,m,c;cin>>n>>m>>c;
    vector<ll>a(n);
    vector<ll>b(m);
    rep(i,n)cin>>a[i];
    rep(i,m)cin>>b[i];
    sort(all(b));
    double ans=0;
    rep(i,n){
        ll p=b.end()-upper_bound(all(b),c/a[i]);
        ans+=(double)p/(double)n/(double)m;
    }
    cout<<fixed<<setprecision(10)<<ans<<endl;
}