#![allow(unused_imports)]
//use itertools::{iproduct, Itertools};
//use proconio::input;
//use proconio::marker::*;
use std::collections::*;

fn is_timataguramu(s: &[i32], t: &[i32]) -> bool {
    let mut kind = 0;
    let mut cnt = 0;
    for i in 0..26 {
        if s[i] > t[i] {
            return false;
        }
        if s[i] == t[i] {
            continue;
        }

        kind += 1;
        cnt += t[i] - s[i];
    }

    kind == 1 && cnt == 1
}

fn main() {
    input! {
        n:usize,
        ss:[chars;n],
    }

    let mut cnts = vec![[0; 26]; n];
    for i in 0..n {
        for &si in &ss[i] {
            cnts[i][(si as u8 - b'a') as usize] += 1;
        }
    }

    for i in 0..n {
        for j in 0..26 {
            cnts[i][j] += 1;
            let mut ok = true;
            for k in 0..n {
                if i == k {
                    continue;
                }

                if is_timataguramu(&cnts[k], &cnts[i]) {
                    ok = false;
                }
            }

            if ok {
                let mut ans = String::new();
                for l in 0..26 {
                    ans += &(std::iter::repeat((l as u8 + b'a') as char)
                        .take(cnts[i][l] as usize)
                        .collect::<String>());
                }
                println!("{}", ans);
                return;
            }

            cnts[i][j] -= 1;
        }
    }

    println!("-1");
}

mod input {
    #[macro_export]
    macro_rules! input {
        (source = $s:expr, $($r:tt)*) => {
            let mut iter = $s.split_whitespace();
            input_inner!{iter, $($r)*}
        };
        ($($r:tt)*) => {
            let s = {
                use std::io::Read;
                let mut s = String::new();
                std::io::stdin().read_to_string(&mut s).unwrap();
                s
            };
            let mut iter = s.split_whitespace();
            input_inner!{iter, $($r)*}
        };
    }

    #[macro_export]
    macro_rules! input_inner {
        ($iter:expr) => {};
        ($iter:expr, ) => {};

        ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
            let $var = read_value!($iter, $t);
            input_inner!{$iter $($r)*}
        };
    }

    #[macro_export]
    macro_rules! read_value {
        ($iter:expr, ( $($t:tt),* )) => {
            ( $(read_value!($iter, $t)),* )
        };

        ($iter:expr, [ $t:tt ; $len:expr ]) => {
            (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
        };

        ($iter:expr, chars) => {
            read_value!($iter, String).chars().collect::<Vec<char>>()
        };

        ($iter:expr, usize1) => {
            read_value!($iter, usize) - 1
        };

        ($iter:expr, $t:ty) => {
            $iter.next().unwrap().parse::<$t>().expect("Parse error")
        };
    }
}