#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,b,,m=0,x;
	float s=0.0;
	int a[100];
	cin>>n;
	for(b=0;b<=n-1;b++){
		cin>>a[b];
	}cin>>x; 
	for(int y=0;y<=n-1;y++){
		if(a[y]==x){
				m++;
		}
	}
	s=m*1.0/n;
	printf("%.2f",s);
	return 0;
}
/**************************************************************
	Problem: 1354
	User: houshanglin
	Language: C++
	Result: Compile Error
****************************************************************/