#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,i,x;
	int m[100];
	float s=0;
	cin>>n;
	for(i=0;i<n;i++){
		cin>>m[i];
	} 
	cin>>x;
	for(i=0;i<n;i++){
		if(x==m[i]){
			s++;
		}
	}
	printf("%.2f",s/n);
	return 0;
}
/**************************************************************
	Problem: 1354
	User: zzz
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/