#include<bits/stdc++.h>
using namespace std;
int main(){
  int i,n,m,x,c=0;
  float b=0;
  int a[30]={0};
  cin>>n;
  for(i=0;i<n;i++) cin>>a[i]; 
  cin>>x;
  for(i=0;i<n;i++){
  if(a[i]==x) c++;
  }
  b=c*1.0/n;
  printf("%.2f ",b);
  return 0;
}
/**************************************************************
	Problem: 1354
	User: wtq001
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/