#!/usr/bin/perl
use v5.35.0;

sub safe {
	return 1 if @_ < 2;		# Reports with only one level are deemed safe
	my $dir = $_[0] <=> $_[1];	# Levels can be either increasing or decreasing
	return 0 if !$dir;		# but not flat
	for (;;) {
		return 0 if abs($_[0] - $_[1]) > 3;	# Change can't be too fast
		shift;
		return 1 if @_ < 2;
		return 0 if ($_[0] <=> $_[1]) != $dir;	# and must be consistent
	}
}

sub problem_dampener {
	return 1 if safe(@_);
	for (0..$#_) {
		return 1 if safe(@_[0..$_-1, $_+1..$#_]);
	}
	return 0;
}

my $safe_count = 0;
while (<>) {
	$safe_count++ if problem_dampener(split);
}
say $safe_count;