В чем проблема?
package com.javarush.task.task18.task1801;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
/*
Максимальный байт
*/
public class Solution {
public static void main(String[] args) throws Exception {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
FileInputStream inputStream = new FileInputStream(reader.readLine());
int sum = 0;
while (inputStream.available() > 0) {
int data = inputStream.read();
sum += data;
}
inputStream.close();
System.out.println(sum);
}
}