<?php
$n = trim(fgets(STDIN));
$a =0;
$b= 0;

if($n % 2 == 1){
    $candy = 2;
}elseif($n % 2 == 0){
    $candy = 1;
}

for($i = 1; $i <= $n;$i++){
    if($i % 2 ==1 && $candy > 0){
        $a++;
        $candy--;
    }elseif($i % 2 == 0 && $candy > 0){
        $b++;
        $candy--;
    }elseif($candy == 0){
        $candy++;
    }
}

echo $a;
?>