Вот решение задачи с "да/нет", которое прошло все тесты.
import java.io.*;
public class test {
public static void main(String[] args) throws FileNotFoundException, IOException {
PrintWriter out;
try (BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream("input.txt"),"UTF-8"))) {
String tempNumber;
String answer = "нет";
while ((tempNumber = in.readLine()) != null) {
try{
if(Integer.parseInt(tempNumber)==7){
answer = "да";
}
}catch(Exception e){}
}
out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(new FileOutputStream("output.txt", false),"cp1251")));
out.print(answer);
}
out.flush();
out.close();
}