<?php
while (true) {
    list($height, $width) = getSpacesByExplodeTrimInput();
    $lines[] = array(); 
    if ($height == 0 && $width == 0) {
        break;
    }
 
    for ($i = 0; $i < $height; $i++) {
        if ($i % 2 !== 0) {
                $lines[] = setEvenNumLine($width);
        } else {
                $lines[] = setOddNumLine($width);
        }
    }

    echo implode($lines), PHP_EOL;
}
 

 
function getSpacesByExplodeTrimInput()
{
    return explode(' ', trim(fgets(STDIN)));
}
 
function setEvenNumLine($width)
{
    $line = "";
    for ($i = 0; $i < $width; $i++) {
        $line .= $i % 2 !== 0 ? "#" : ".";
    }
    return $line.PHP_EOL;
}
 
function setOddNumLine($width)
{
    $line = "";
    for ($i = 0; $i < $width; $i++) {
        $line .= $i % 2 !== 0 ? "." : "#";
    }
    return $line.PHP_EOL;
}