<?php

$elves = explode("\n", file_get_contents('./input.txt'));

echo count(
    array_filter(
        $elves,
        static function($elf) {
            [$section1, $section2] = array_map(static fn($section) => explode('-', $section), explode(',', $elf));
            return count(
                array_intersect(range($section1[0], $section1[1]), range($section2[0], $section2[1]))
            ) > 0;
        }
    )
);