get count of (nineteen) word in random string

nineteenTask.php

<?php

$str = "nnteirnnyeutbneveectnifngninejtfeesexn";
$strlen = strlen( $str );

$nChar = 0;
$iChar = 0;
$eChar = 0;
$tChar = 0;

for( $i = 0; $i <= $strlen; $i++ ) {
    $char = substr( $str, $i, 1 );

    if($char == 'n'){
    	$nChar++;	
    }elseif($char == 'i'){
    	$iChar++;
    }elseif($char == 'e'){
    	$eChar++;
    }elseif($char == 't'){
    	$tChar++;
    }

}

if($nChar < $eChar){
	if(($iChar && $tChar) >= $nChar / 3){
		echo round($nChar / 3);
	}
}else{
	if(($iChar && $tChar) >= $eChar / 3){
		echo round($eChar / 3);
	}
}