https://www.acmicpc.net/problem/30456

그냥 1을 L-1개 출력하고 N을 출력하면 됩니다.
import java.util.*;
import java.io.*;
public class Main {
public static void main(String[] args) throws Exception{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st = new StringTokenizer(br.readLine());
int N = Integer.parseInt(st.nextToken());
int L = Integer.parseInt(st.nextToken());
for(int i = 0; i < L - 1; i ++){
System.out.print(1);
}
System.out.print(N);
}
}