36. According to legend, in ancient times, there were nine-headed birds and nine-tailed birds living together on the mysterious Phoenix Mountain. The nine-headed bird has nine heads and one tail, while the nine-tailed bird has nine tails and one head. If there are a total of 115 heads and 155 tails on Phoenix Mountain, then there are $\qquad$ nine-headed birds living on Phoenix Mountain.
$11$