<?php

$testCases = intval(fgets(STDIN));

for ($i = 1; $i <= $testCases; $i++) {
    $params = explode(" ", fgets(STDIN));
    $M = intval($params[0]); // length of freeway
    $R = intval($params[1]); // illumination radius of lightbulbs
    $N = intval($params[2]); // number of street lights
    $positions = array_map('intval', explode(" ", fgets(STDIN))); // positions of street lights

    $bulbCount = 0;
    $lastBulbPos = -1;

    foreach ($positions as $pos) {
        if ($pos <= $lastBulbPos) {
            continue;
        }

        $leftMost = max(0, $pos - $R);
        $rightMost = min($M, $pos + $R);

        while ($lastBulbPos >= 0 && $positions[$lastBulbPos] >= $leftMost) {
            $lastBulbPos--;
        }

        if ($lastBulbPos < 0 || $positions[$lastBulbPos] < $pos - $R) {
            $lastBulbPos = array_search(max($positions), $positions);
            $bulbCount++;
        } else {
            $bulbCount++;
        }

        if ($positions[$lastBulbPos] > $rightMost) {
            break;
        }
    }

    if ($positions[$lastBulbPos] < $M) {
        echo "Case #{$i}: IMPOSSIBLE\n";
    } else {
        echo "Case #{$i}: {$bulbCount}\n";
    }
}