telefone

#include <bits/stdc++.h>

using namespace std;

int resp;

struct node{
    bool end;
    bool ponte;
    int pass;
    struct node* word[26];
} *head;

void init(){
    head = new node();
    head->ponte = false;
    head->end = false;
    head->pass = 0;
}

void add(string palavra){
    node* current = head;
    bool create = false;
    for(int i = 0; i < palavra.size(); i++){
        //cout << palavra[i] << " ";
        int letra = palavra[i]-(int)'a';

        current->pass++;
        if(current->ponte){
            resp++;
            //cout << "ponte ";
        }

        if(current->word[letra] == NULL){
            current->word[letra] = new node();

            if(!create && i){
                //cout << "criado ";
                if(!current->ponte){
                    //cout << "dividido ";
                    resp += current->pass;
                    current->ponte = true;
                }
            }
            create = true;
        }

        current = current->word[letra];
        cout << endl;
    }
    if(!create && !current->ponte){
            //cout << "final em meio\n";
            resp++;
            current->ponte = true;
    }
    current->end = true;
}


int main(){
    int num;
    while(cin>> num){
        init();
        resp = 0;
        for(int i = 0; i < num; i++){
            string palavra; cin >> palavra;
            add(palavra);
        }
        //cout << resp << endl;
        printf("%.2f\n",(resp+num)/(double)num);
    }
    return 0;
}