For those who are not familiar with file IO, there are several solutions of "A*B" problem in some popular programming languages:

Pascal / Delphi:

var
    a, b: longint;
begin
    assign(input, 'input.txt');
    assign(output, 'output.txt');
    reset(input);
    rewrite(output);
    read(a, b);
    writeln(a * b);
    close(input);
    close(output);
end.

C/C++:
#include <stdio.h>
int main()
{
    int a, b;

    freopen("input.txt", "rt", stdin);
    freopen("output.txt", "wt", stdout);

    scanf("%d %d", &a, &b);
    printf("%d\n", a * b);
    
    return 0;
}

Java:
import java.io.*;
import java.util.*;

public class Solution {
    public static void main(String[] args) throws FileNotFoundException {
        Scanner s = new Scanner(new File("input.txt"));
        int a = s.nextInt();
        int b = s.nextInt();
        s.close();

        PrintWriter writer = new PrintWriter("output.txt");
        writer.println(a * b);
        writer.close();
    }
}