Wydaje mi się że jest poprawnie, ale mogę się mylić.
package pl.codegym.task.task18.task1801;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;
/*
Maksymalna liczba bajtów
*/
public class Solution {
public static void main(String[] args) throws Exception {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
FileInputStream fileInputStream = new FileInputStream(new File(bufferedReader.readLine()));
ArrayList list = new ArrayList();
while (fileInputStream.available()>0){
list.add(fileInputStream.read());
}
System.out.println(Collections.max(list));
bufferedReader.close();
fileInputStream.close();
}
}