How can I create PDF document in R Markdown with cyrillc font

rmarkdown

#1

I have a preamble

---
title: "Title"
author: "Me"
output:
    pdf_document:
        keep_tex: yes
header-includes:
   - \usepackage[T2A]{fontenc}
   - \usepackage[utf8]{inputenc}
   - \usepackage[russian]{babel}


---

but it doesn't work with Cyrillic font. Please? can you say where is problem?