Use the given jQuery code in document_ready block.
Sample
var modal_lv = 10000;
$('.modal').on('shown.bs.modal', function (e) {
$('.modal-backdrop:last').css('zIndex', 1051 + modal_lv);
$(e.currentTarget).css('zIndex', 1052 + modal_lv);
modal_lv++
});
$('.modal').on('hidden.bs.modal', function (e) {
modal_lv--
});
Sample