#ifdef ONLINE_JUDGE
#pragma GCC target("avx2,avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#endif
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using i128 = __int128_t;
using pii = pair<int, int>;
using pll = pair<long long, long long>;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define all(x) (x).begin(), (x).end()
constexpr char ln = '\n';
istream& operator>>(istream& is, __int128_t& x) {
    x = 0;
    string s;
    is >> s;
    int n = int(s.size()), it = 0;
    if (s[0] == '-') it++;
    for (; it < n; it++) x = (x * 10 + s[it] - '0');
    if (s[0] == '-') x = -x;
    return is;
}
ostream& operator<<(ostream& os, __int128_t x) {
    if (x == 0) return os << 0;
    if (x < 0) os << '-', x = -x;
    deque<int> deq;
    while (x) deq.emplace_front(x % 10), x /= 10;
    for (int e : deq) os << e;
    return os;
}
template<class T1, class T2>
ostream& operator<<(ostream& os, const pair<T1, T2>& p) {
    return os << "(" << p.first << ", " << p.second << ")";
}
template<class T> 
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "{";
    for (int i = 0; i < int(v.size()); i++) {
        if (i) os << ", ";
        os << v[i];
    }
    return os << "}";
}
template<class Container> inline int SZ(Container& v) { return int(v.size()); }
template<class T> inline void UNIQUE(vector<T>& v) { v.erase(unique(v.begin(), v.end()), v.end()); }
template<class T1, class T2> inline bool chmax(T1& a, T2 b) { if (a < b) {a = b; return true ;} return false ;}
template<class T1, class T2> inline bool chmin(T1& a, T2 b) { if (a > b) {a = b; return true ;} return false ;}
inline int topbit(int x) { return x == 0 ? -1 : 31 - __builtin_clz(x); }
inline int topbit(long long x) { return x == 0 ? -1 : 63 - __builtin_clzll(x); }
inline int botbit(int x) { return x == 0 ? 32 : __builtin_ctz(x); }
inline int botbit(long long x) { return x == 0 ? 64 : __builtin_ctzll(x); }
inline int popcount(int x) { return __builtin_popcount(x); }
inline int popcount(long long x) { return __builtin_popcountll(x); }
inline int kthbit(long long x, int k) { return (x>>k) & 1; }
inline constexpr long long TEN(int x) { return x == 0 ? 1 : TEN(x-1) * 10; }
inline void print() { cout << "\n"; }
template<class T>
inline void print(const vector<T>& v) {
    for (int i = 0; i < int(v.size()); i++) {
        if (i) cout << " ";
        cout << v[i];
    }
    print();
}
template<class T, class... Args>
inline void print(const T& x, const Args& ... args) {
    cout << x << " ";
    print(args...);
}
#ifdef MINATO_LOCAL
inline void debug_out() { cerr << endl; }
template <class T, class... Args>
inline void debug_out(const T& x, const Args& ... args) {
    cerr << " " << x;
    debug_out(args...);
}
#define debug(...) cerr << __LINE__ << " : [" << #__VA_ARGS__ << "] =", debug_out(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " : " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif
struct fast_ios { fast_ios() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

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];

    ll cnt = 0;
    sort(all(B));
    reverse(all(B));
    rep(i,N) {
        auto check=[&](int mid) {
            return A[i]*B[mid] > C;
        };
        int ok = -1;
        int ng = M;
        while (ng-ok>1) {
            int mid = (ok+ng)/2;
            (check(mid) ? ok : ng) = mid;
        }
        cnt += ng;
    }

    cout << (double)cnt/(N*M) << ln;
}