#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define rep(i,m,n) for(int i=m; i<int(n); ++i)
#define repll(i,m,n) for(ll i=m; i<ll(n); ++i)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define leng(a) int(a.size())
#define fi first
#define se second

template<typename T> bool chmin(T& a, T b){ if(a > b){a = b; return true;} return false; }
template<typename T> bool chmax(T& a, T b){ if(a < b){a = b; return true;} return false; }

template<typename T> T gcd(T a, T b){ return a % b ? gcd(b, a % b) : b; }
template<typename T> T lcm(T a, T b){ return a / gcd(a, b) * b; }

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N, M;
    ll C;
    cin >> N >> M >> C;
    vector<ll> A(N), B(M);
    rep(i, 0, N) cin >> A[i];
    rep(i, 0, M) cin >> B[i];

    sort(all(B));
    ll ans = 0LL;
    rep(i, 0, N){
        if(A[i]*B[0] > C){
            ans += ll(M);
            continue;
        }
        if(A[i]*B[M-1] <= C) continue;
        
        int l = 0, h = M-1, m;
        while(h - l > 1){
            m = (h + l) / 2;
            (A[i]*B[m] > C ? h : l) = m;
        }
        // cout << i << ' ' << h << endl;
        ans += ll(M - h);
    }

    printf("%.10f\n", double(ans)/double(N*M));
    return 0;
}