import java.util.*; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); int m = sc.nextInt(); long c = sc.nextLong(); int[] aArr = new int[n]; for (int i = 0; i < n; i++) { aArr[i] = sc.nextInt(); } Arrays.sort(aArr); int[] bArr = new int[m]; for (int i = 0; i < m; i++) { bArr[i] = sc.nextInt(); } long count = 0; int idx = m; for (int i = 0; i < n; i++) { while (idx > 0 && (long)aArr[i] * bArr[idx - 1] > c) { idx--; } count += m - idx; } System.out.println((double)count / n / m); } }