<?php

$jsonY = '{"years": {
        "2016": [1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0],
        "2017": [0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0],
        "2018": [0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0],
        "2019": [0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0],
        "2020": [0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0],
        "2008": [0, 0, 0, 0, 0, 0, 0, 1, 7, 6, 4, 6],
        "2009": [1, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        "2010": [0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        "2011": [0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        "2013": [1, 0, 0, 3, 3, 0, 0, 0, 0, 0, 0, 0],
        "2014": [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        "2015": [0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0]
    }}';

$arrayY = json_decode($jsonY, true);
$count = 0;
foreach ($arrayY['years'] as $year){
    $count += array_sum($year);
}

echo $count;

?>