#include <iostream>
#include <vector>
#include <iomanip>
#include <fstream>

using namespace std;


class fa{
public:
long double perms;
int value;
fa * left;
fa* right;
int elems;
};


/*
class holder{
public:	fa * root;
};*/

void makefactorial(vector<long double>& fack){
	fack.push_back(1);
	for(int i=1;i<101;++i){
		fack.push_back(fack.at(i-1)*i);
	}
};

fa* insert(int elem, fa* tree){
	if(!tree){
		fa* ujfa = new fa;
		ujfa->left = NULL;
		ujfa->right = NULL;
		ujfa->value = elem;
		ujfa->elems = 0;
		ujfa->perms = 0;
		return ujfa;
	}else{
		if(elem<tree->value){
			tree->left = insert(elem,tree->left);
		}else{	tree->right = insert(elem,tree->right);
		};
		return tree;
	}
}


long double value(fa* tree,vector<long double>& factorial){
	if(tree->left == NULL && tree->right == NULL){
		tree->elems = 1;
//		cout << "elem " << tree->value << " elesm " << tree->elems << endl;	
		return 1;
	}else{
		if(tree->left == NULL || tree->right == NULL){
			fa* alfa = (tree->left == NULL ? tree->right : tree->left);
			
			long double ize = value(alfa,factorial);
			tree->elems = alfa->elems + 1;
//			cout << "elem " << tree->value << " perm " << ize << "alfaelems " << alfa->elems << "elems " << tree->elems << endl;			
			return ize ; //value(alfa,factorial);
		}else{
			
			long double ize = value(tree->left,factorial) * value(tree->right,factorial) * factorial.at(tree->left->elems + tree->right->elems) / factorial.at(tree->left->elems) / factorial.at(tree->right->elems);
			tree->elems = tree->left->elems +  tree->right->elems +1;
 // 			cout << "elem " <<  tree->value << " perm " <<ize << "leftelems "<< tree->left->elems << " rightelems " << tree->right->elems << " asd " << factorial.at(tree->left->elems + tree->right->elems) << " " << factorial.at(tree->left->elems) << " " << factorial.at(tree->right->elems) << " ize"  << " elems " << tree->elems << endl;

			return ize;
		}
	}
		
};



int main(){
	int num;
	int elem;
	cin >> num;
	fa* tree = NULL;
	vector<long double> factorial;
	makefactorial(factorial);

	while(num){
		for (int i=0;i<num;++i){
			cin >> elem;
			tree = insert(elem,tree);		
		}
		//printf("%i\n",value(tree, factorial));
		cout.precision( 32 );
		cout << value(tree,factorial) << endl;	
		cin >> num;
	}
	
	return 0;
}