#include using namespace std; #define rep(i, n) for(int(i) = 0; (i) < (n); (i)++) #define FOR(i, m, n) for(int(i) = (m); (i) < (n); (i)++) #define All(v) (v).begin(), (v).end() #define pb push_back #define MP(a, b) make_pair((a), (b)) template vector make_vec(size_t a, T val) { return vector(a, val); } template auto make_vec(size_t a, Ts... ts) { return vector(a, make_vec(ts...)); } using ll = long long; using pii = pair; using pll = pair; using Graph = vector>; template struct edge { int to; T cost; edge(int t, T c) : to(t), cost(c) {} }; template using WGraph = vector>>; const int INF = 1 << 30; const ll LINF = 1LL << 60; const int MOD = 1e9 + 7; int main() { int N, M; ll C; cin >> N >> M >> C; vector A(N), B(M); rep(i, N) cin >> A[i]; rep(i, M) cin >> B[i]; sort(All(A)); reverse(All(A)); sort(All(B)); ll cur = 0; ll Bwin = 0; for(int i = 0; i < N; i++) { while(cur < M && A[i] * B[cur] <= C) cur++; Bwin += cur; } cout << fixed << setprecision(10) << (double)(N * M - Bwin) / (double)(N * M) << endl; }