Measuring the speed of different 
computational configurations



function s1(arg){
 var res = 0;
 
 ////
  for(var i = 1; i <= arg; i++)
   if(i%3==0)res+=i;
 /////

  console.log(res);
}


function s2(arg){
  var res = 0;
  
  ////
  var x = Math.floor(arg/3)*3;
  for(var i = 0; i <= x; i+=3)
    res+=i;
  ////
  
console.log(res);
}

function s3(arg){
  var res = 0;
  
  ////
  var x = Math.floor(arg/3);
  res = x*(3+x*3)/2
  ////
  
console.log(res);
}



console.time("s1");s1(123456789);console.timeEnd("s1");
console.time("s2");s2(123456789);console.timeEnd("s2");
console.time("s3");s3(123456789);console.timeEnd("s3");