import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.NoSuchElementException;

public class Main {
	public static void main(String args[]) {
		FastScanner scanner = new FastScanner();
		int n=scanner.nextInt();
		int[] a=new int[n];
		int[] b=new int[n];
		for(int i=0;i<n;i++) {
			a[i]=scanner.nextInt();
		}
		for(int i=0;i<n;i++) {
			b[i]=scanner.nextInt();
		}
		Arrays.sort(a);
		Arrays.sort(b);
		int cnt=0;
		do {
			do {
				int tmp=0;
				for(int i=0;i<n;i++) {
					if(a[i]>b[i])tmp++;
				}
				if(tmp>n/2)cnt++;
			}while(next_permutation(b));
			Arrays.sort(b);
		}while(next_permutation(a));
		long f=factorial(n);
		System.out.println((double)cnt/(f*f));
	}
	
	private static boolean next_permutation(int[] p) {
		for (int a = p.length - 2; a >= 0; --a) {
			if (p[a] < p[a + 1]) {
				for (int b = p.length - 1;; --b) {
					if (p[b] > p[a]) {
						int t = p[a];
						p[a] = p[b];
						p[b] = t;
						for (++a, b = p.length - 1; a < b; ++a, --b) {
							t = p[a];
							p[a] = p[b];
							p[b] = t;
						}
						return true;
					}
				}
			}
		}
		return false;
	}
	
	static long factorial(int n){
		long s = 1;
		for (int i = 1; i <= n; i++)
			s *= i;
			return s;
	}
}


class FastScanner {
    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();}
    public 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();
    }
    public 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();
        }
    }
    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }
    public double nextDouble() { return Double.parseDouble(next());}
}