<script>
kmh=setInterval(
function Time_admin()
{
d=((document.getElementById('n1').innerHTML)*1);
S=((document.getElementById('kms').innerHTML)*1);

var chbox;
chbox=document.getElementById('payt4');

if (chbox.checked) 
{
var q;
A=document.getElementById('km').innerHTML;
a=((A)*1);
q=((5)*1);
T=((a+q)*1);
{
document.getElementById("km").innerHTML=T;


if (A==500 )
{
switch(d) 
{ 
case 1:   
Ost1();
break;
case 2:   
Ost2();
break;
case 3: 
Ost3();
break;
case 9:   
Ost9();
break;
case 4:   
Ost4();
break;
case 7:   
Ost7();
break;
case 6:   
Ost6();
break;
}
document.getElementById('km').innerHTML=0;
document.getElementById("kms").innerHTML=(S+500);
}
}
} 
else
{

}
},100)
</script>

<div id="km">0</div>
<script>
const limit = 500, durationPause = 2000, durationStep = 10;
let num = 0;

(function animateNum()
{
   km.innerHTML = ++num;
   window.setTimeout(animateNum,num % limit ? durationStep : durationPause)
})()
</script>