#include<iostream> #include<string> #include<vector> #include<algorithm> #include<bitset> #include<set> #include<map> #include<stack> #include<queue> #include<deque> #include<list> #include<iomanip> #include<cmath> #include<cstring> #include<functional> #include<cstdio> #include<cstdlib> #include<numeric> using namespace std; #define repr(i, a, b) for (int i = (int)(a); i < (int)(b); i++) #define rep(i, n) repr(i, 0, n) #define INF 2e9 //#define MOD 1000000007 #define MOD 998244353 #define LINF (long long)4e18 #define jck 3.141592 #define PI acos(-1.0) const double EPS = 1e-10; using ll = long long; using Pi = pair<int,int>; using Pl = pair<ll,ll>; int main(){ ll n,m,c; cin >> n >> m >> c; vector<ll> a(n),b(m); rep(i,n) cin >> a[i]; rep(i,m) cin >> b[i]; sort(b.begin(),b.end()); ll sum = 0; rep(i,n){ int d = lower_bound(b.begin(),b.end(),c/a[i]+1)-b.begin(); sum += m-d; } cout << fixed << setprecision(10); cout << (double)sum/(n*m) << endl; }