//https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 より
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_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_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, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

//

fn run() {
    input! {
        s: bytes,
        t: bytes,
    }
    let p = 26;
    let mut index = vec![vec![vec![]; p]; 2];
    for (index, s) in index.iter_mut().zip([&s, &t].iter()) {
        for (i, s) in s.iter().enumerate() {
            let k = (*s - b'a') as usize;
            index[k].push(i);
        }
    }
    let mut dp = vec![None; s.len() + 1];
    dp[s.len()] = Some(t.len());
    let mut i = s.len();
    while i > 0 {
        i -= 1;
        let x = dp[i + 1].unwrap();
        if x == 0 {
            break;
        }
        let k = (s[i] - b'a') as usize;
        let y = match index[1][k].binary_search(&(x - 1)) {
            Ok(y) => index[1][k][y],
            Err(y) if y == 0 => break,
            Err(y) => index[1][k][y - 1],
        };
        dp[i] = Some(y);
    }
    if dp[0].is_some() {
        println!("-1");
        return;
    }
    let mut ans = String::new();
    let mut i = 0;
    let mut j = 0;
    'outer: while dp[i].map_or(true, |p| p < j) {
        for k in 0..26 {
            let x = match index[0][k].binary_search(&i) {
                Ok(x) => index[0][k][x],
                Err(x) if x < index[0][k].len() => index[0][k][x],
                _ => continue,
            };
            let y = match index[1][k].binary_search(&j) {
                Ok(x) => index[1][k][x],
                Err(x) if x < index[1][k].len() => index[1][k][x],
                _ => {
                    ans.push((b'a' + k as u8) as char);
                    break 'outer;
                },
            };
            if dp[x + 1].map_or(true, |p| p < y + 1) {
                ans.push((b'a' + k as u8) as char);
                i = x + 1;
                j = y + 1;
                break;
            }
        }
    }
    println!("{}", ans);
}

fn main() {
    run();
}