function gbqagbjk() {
  if(window.innerHeight) {
    document.getElementById("obsah").style.minHeight = (window.innerHeight - 206) + "px";
  } else {
    document.getElementById("obsah").style.height = (document.body.clientHeight - 200) + "px";
  };
}

gbqagbjk();

window.onresize = gbqagbjk;