#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);
}
/**************************************************************
	Problem: 1354
	User: linzihang
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/