import java.util.*; import java.io.*; import java.math.*; class Main{ void solve(PrintWriter out , In in) { // A * B < C -> A < C / B int n = in.nextInt() , m = in.nextInt() ; long c = in.nextLong(); long [] a = in.LongArray(n); long [] b = in.LongArray(m); Arrays.sort(a); Arrays.sort(b); long bottom = n * m ; long ok = 0 ; for(int i = 0 ; i < m ; i ++ ) { int p = upper_bound(a , c / b[i]); ok += (n - p) ; } out.print((double) ok / bottom); } int upper_bound(long [] A , long key) { int left = 0; int right = A.length; while(left < right) { int mid = (left + right) / 2; if(A[mid] <= key) left = mid + 1; else right = mid; } return right; } public static void main(String[] args) { PrintWriter pw = new PrintWriter(System.out); In in = new In(); new Main().solve(pw,in); pw.flush(); } } class Pair, U extends Comparable> implements Comparable> { private final T first; private final U second; Pair(T first, U second) { this.first = first; this.second = second; } T first() { return first; } U second() { return second; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Pair pair = (Pair) o; return Objects.equals(first, pair.first) && Objects.equals(second, pair.second); } @Override public int hashCode() { return Objects.hash(first, second); } @Override public int compareTo(Pair other) { T small_First = this.first , large_First = other.first; U small_Second = this.second , large_Second = other.second; int First_Result = small_First.compareTo(large_First); int Second_Result = small_Second.compareTo(large_Second); return First_Result == 0 ? Second_Result : First_Result ; } @Override public String toString() { return this.first+" "+this.second; } } class Triple, U extends Comparable, V extends Comparable> implements Comparable> { private final T first; private final U second; private final V third; Triple(T first, U second, V third) { this.first = first; this.second = second; this.third = third; } T first() { return first; } U second() { return second; } V third() { return third; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Triple triple = (Triple) o; return Objects.equals(first, triple.first) && Objects.equals(second, triple.second) && Objects.equals(third, triple.third) ; } @Override public int hashCode() { return Objects.hash(first, second, third); } @Override public int compareTo(Triple other) { T small_First = this.first , large_First = other.first; U small_Second = this.second , large_Second = other.second; V small_Third = this.third , large_Third = other.third; int First_Result = small_First.compareTo(large_First); int Second_Result = small_Second.compareTo(large_Second); int Third_Result = small_Third.compareTo(large_Third); return First_Result == 0 ? (Second_Result == 0 ? Third_Result : Second_Result ) : First_Result; } } class In{ private final InputStream in = System.in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; private boolean hasNextByte() { if (ptr < buflen) { return true; }else{ ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } if (buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1; } private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126; } public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) { ptr++; } return hasNextByte(); } String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while(isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } long nextLong() { if (!hasNext()) throw new NoSuchElementException(); long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) { throw new NumberFormatException(); } while(true){ if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; }else if(b == -1 || !isPrintableChar(b)){ return minus ? -n : n; }else{ throw new NumberFormatException(); } b = readByte(); } } int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException(); return (int) nl; } double nextDouble() { return Double.parseDouble(next()); } char nextChar() { return next().charAt(0); } int [] IntArray(int n) { final int [] Array = new int [n]; for(int i = 0 ; i < n ; i ++ ) { Array[i] = nextInt(); } return Array; } int [][] IntArray(int n , int m) { final int [][] Array = new int [n][m]; for(int i = 0 ; i < n ; i ++ ) { Array[i] = IntArray(m); } return Array; } long [] LongArray(int n) { final long [] Array = new long [n]; for(int i = 0 ; i < n ; i ++ ) { Array[i] = nextLong(); } return Array; } long [][] LongArray(int n , int m) { final long [][] Array = new long [n][m]; for(int i = 0 ; i < n ; i ++ ) { Array[i] = LongArray(m); } return Array; } String [] StringArray(int n) { final String [] Array = new String [n]; for(int i = 0 ; i < n ; i ++ ) { Array[i] = next(); } return Array; } char [] CharArray(int n) { final char [] Array = new char[n]; for(int i = 0 ; i < n ; i ++ ) { Array[i] = next().charAt(0); } return Array; } char [][] CharArray(int n , int m) { final char [][] Array = new char [n][m]; for(int i = 0 ; i < n ; i ++ ) { Array[i] = next().toCharArray(); } return Array; } char [][] CharArray2(int n , int m) { final char [][] Array = new char [n][m]; for(int i = 0 ; i < n ; i ++ ) { for(int j = 0 ; j < n ; j ++ ) { Array[i][j] = next().charAt(0); } } return Array; } }