var i = 2;
while(i < n + 1) {
  alert (i.toString() + " Ahoj");   
  i = i + 2;
}

var i = 2;
do {
  alert (i.toString() + " Ahoj"); 
  i = i + 2;
}
while(i < n + 1);

var i = 2;
for (i = 2; i < n + 1; i = i + 2) {
  alert (i.toString() + " Ahoj");    
}