function main() {
  var numAst = document.getElementById('numeroDeAsteriscos').value;
  for (let a = 1; a < numAst; a++) {

    for (let i = 0; i < a; i++) {
      document.writeln(`*`);
    }
    document.writeln(`<br>`)

  }
  for (let i = 0; i < numAst / 2; i++) {
    document.writeln(`*<br>`)
  }
}