package Practice;

import java.io.BufferedReader;

import java.io.InputStreamReader;

import java.util.HashMap;

public class B5670 { //ÈÞ´ëÆù ÀÚÆÇ

static double count;

public static void main(String[] args) throws Exception {

// TODO Auto-generated method stub

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

StringBuilder sb = new StringBuilder();

String T;

while((T = br.readLine()) != null) {

count = 0;

int N = Integer.parseInt(T);

Trie trie = new Trie();

for(int i = 0; i < N; i++) trie.insert(br.readLine());

trie.search();

count /= N;

sb.append(String.format("%.2f", count)).append('\n');

}

System.out.println(sb);

}

static class Trie {

private TrieNode Node = new TrieNode();

void insert(String str) {

TrieNode node = this.Node;

for(int i = 0; i < str.length(); i++) {

node = node.childNode.computeIfAbsent(str.charAt(i), key -> new TrieNode());

node.count++;

}

node.lastNode = true;

}

private void search(TrieNode node) {

if(node.lastNode) {

for(Character word : node.childNode.keySet()) {

TrieNode tempNode = node.childNode.get(word);

search(tempNode);

count += tempNode.count;

}

return;

}

if(node.childNode.size() == 1) {

for(Character word : node.childNode.keySet()) {

TrieNode tempNode = node.childNode.get(word);

search(tempNode);

}

}

else {

for(Character word : node.childNode.keySet()) {

TrieNode tempNode = node.childNode.get(word);

search(tempNode);

count += tempNode.count;

}

}

}

void search() {

for(Character word : Node.childNode.keySet()) {

TrieNode tempNode = Node.childNode.get(word);

search(tempNode);

count += tempNode.count;

}

}

}

static class TrieNode {

private HashMap<Character, TrieNode> childNode;

boolean lastNode;

int count;

TrieNode() {

childNode = new HashMap<>();

}

}

}