use proconio::{input, marker};

fn main() {
    input! {
        s: marker::Bytes,
        t: marker::Bytes,
        n: usize,
    }
    let mut ans = s;
    for _ in 0..n {
        ans.push(b'_');
        ans.extend(t.iter().copied());
    }
    println!("{}", std::str::from_utf8(&ans).unwrap());
}