#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,i,a[100],x,s=0;
	double s1=0;
	cin>>n;
	for (i=0;i<n;i++) {
		cin>>a[i];
	}
	cin>>x;
	for (i=0;i<n;i++) {
		if (a[i]==x) {
			s++;
		}
	}
	s1=s*1.0/n;
	cout<<fixed<<setprecision(2)<<s1<<endl;

	return 0;
}

/**************************************************************
	Problem: 1354
	User: admin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/