$m=1e9+7;
$n=<>;
@e=<>;
for$d(d00,d01,d10,d11){
	$d00=0;
	$d01=0;
	$d10=0;
	$d11=0;
	$$d=1;
	for(@e){
		if($_!=0){
			$e00=0;
			$e01=$d00+$d10;
			$e10=$d01+$d11;
			$e11=$d01;
		}else{
			$e00=$d00+$d10;
			$e01=0;
			$e10=0;
			$e11=$d11;
		}
		$d00=$e00%$m;
		$d01=$e01%$m;
		$d10=$e10%$m;
		$d11=$e11%$m;
	}
	$r+=$$d;
}
print$r%$m;