#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int i=0; i<(int)n; i++)
#define rep1(i,n) for(int i=1; i<(int)n; i++)
#define repa(i,a,n) for(int i=(a); i<(int)(n); i++)
#define all(vec) vec.begin(),vec.end()
#define COUT(x) cout<<(x)<<endl
#define YES(x) cout<<(x?"YES":"NO")<<endl
#define Yes(x) cout<<(x?"Yes":"No")<<endl
#define F first
#define S second
using vi = vector<int>;
using vs = vector<string>;
using vvi = vector<vi>;
using pii = pair<int, int>;
using vpii = vector<pii>;
const int dx[4] = {1, 0,-1, 0};
const int dy[4] = {0, 1, 0,-1};
int gcd(int a, int b){if(a%b == 0){return(b);}else{return(gcd(b, a%b));}}
int lcm(int a, int b){return a/gcd(a, b)*b;}
template <typename T> bool chmax(T &a,const T& b){if(a<b){a=b;return true;}return false;}
template <typename T> bool chmin(T &a,const T& b){if(a>b){a=b;return true;}return false;}
//cout << fixed << setprecision(15);
int N, M, K, H, W, X, Y;
string S,T;
const int INF = 1e18;
const int mod = 1e9+7;

signed main(){
    int C;
    cin >> N >> M >> C;
    vi A(N); rep(i,N){cin >> A[i];}
    sort(all(A));
    vi B(M); rep(i,M) cin >> B[i];
    sort(all(B));
    double ans = 0;
    rep(i,N){
        if(B.size()==1){
            if(B[0]*A[i]>C) ans++;
            continue;
        }

        int l = 0; int r = M;
        while(l+1 != r){
            int s = (l+r)/2;
            if(A[i]*B[s]>C) r = s;
            else l = s;
        }
        if(l==0) ans += M;
        else if(l== M-1) continue;
        else ans += M-r;
    }
    cout << fixed << setprecision(15);
    COUT(ans/(N*M));
    return 0;
}