#![allow(unused_imports)]

use std::cmp::{max, min, Ordering};
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, VecDeque};
use std::io::stdin;
use std::ops::*;
use std::process::exit;
use std::str::FromStr;

/// 配列に含まれる要素(T: Ord + Copy)別にその個数を数えて
/// `BTreeMap<T, usize>`の形にして返す
pub fn unique_count<T: Ord + Copy>(v: &[T]) -> BTreeMap<T, usize> {
    let mut map = BTreeMap::new();
    for e in v {
        let h = map.entry(*e).or_insert(0);
        *h += 1;
    }
    map
}

const A: u8 = 'a' as u8;

fn main() {
    let n: usize = input();
    let ss: Vec<Vec<char>> = input_lines(n)
        .iter()
        .map(|x: &String| x.chars().collect::<Vec<char>>())
        .collect();

    let mut ans = vec![None; 26];
    for s in ss {
        let mut count = vec![0; 26];
        for i in s {
            count[(i as u8 - A) as usize] += 1;
        }

        for i in 0..26 {
            ans[i] = Some(min(ans[i].unwrap_or(std::usize::MAX), count[i]));
        }
    }

    let mut s = String::new();
    for (o, c) in ans.into_iter().enumerate() {
        match c {
            Some(c) => {
                for i in 0..c {
                    s.push((A + o as u8) as char);
                }
            }
            None => {}
        }
    }

    println!("{}", s);
}

pub fn input<T: FromStr>() -> T {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();
    buf.trim().parse().ok().unwrap()
}

pub fn input_vec<T: FromStr>() -> Vec<T> {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();
    buf.trim()
        .split_whitespace()
        .map(|x| x.parse().ok().unwrap())
        .collect::<Vec<_>>()
}

pub fn input_lines<T: FromStr>(l: usize) -> Vec<T> {
    let mut res = Vec::new();
    for _i in 0..l {
        res.push(input());
    }
    res
}

pub fn input_lines_two<T: FromStr, U: FromStr>(l: usize) -> Vec<(T, U)> {
    let mut res = Vec::new();
    for _i in 0..l {
        res.push(input_two());
    }
    res
}

pub fn input_lines_three<T: FromStr, U: FromStr, V: FromStr>(l: usize) -> Vec<(T, U, V)> {
    let mut res = Vec::new();
    for _i in 0..l {
        res.push(input_three());
    }
    res
}

pub fn input_two<T: FromStr, U: FromStr>() -> (T, U) {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();
    let s: Vec<&str> = buf.split_whitespace().collect();
    (
        s[0].parse::<T>().ok().unwrap(),
        s[1].parse::<U>().ok().unwrap(),
    )
}

pub fn input_three<T: FromStr, U: FromStr, V: FromStr>() -> (T, U, V) {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();
    let s: Vec<&str> = buf.split_whitespace().collect();
    (
        s[0].parse::<T>().ok().unwrap(),
        s[1].parse::<U>().ok().unwrap(),
        s[2].parse::<V>().ok().unwrap(),
    )
}

pub fn input_four<T: FromStr, U: FromStr, V: FromStr, W: FromStr>() -> (T, U, V, W) {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();
    let s: Vec<&str> = buf.split_whitespace().collect();
    (
        s[0].parse().ok().unwrap(),
        s[1].parse().ok().unwrap(),
        s[2].parse().ok().unwrap(),
        s[3].parse().ok().unwrap(),
    )
}


Measured memory_bytes: 4352