Вот сама ошибка - при вводе любого символа, в данном случае 2; Exception in thread "main" java.io.FileNotFoundException: 2 (Не удается найти указанный файл) at java.io.FileInputStream.open0(Native Method) at java.io.FileInputStream.open(FileInputStream.java:195) at java.io.FileInputStream.<init>(FileInputStream.java:138) at java.io.FileInputStream.<init>(FileInputStream.java:93) at com.javarush.task.task18.task1802.Solution.main(Solution.java:16) Сам код решения =>
package com.javarush.task.task18.task1802;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;

/*
Минимальный байт
*/

public class Solution {
    public static void main(String[] args) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String str = reader.readLine();
        int min = 255;
        try(FileInputStream stream = new FileInputStream(str)){
            while (stream.available() > 0){
                int buff = stream.read();
                if (min > buff) {
                    min = buff;
                }
            }
        }
        System.out.println(min);
    }
}