A Welcome Mat

Copy and paste the script:-

string previously_Welcomed;
default
{
touch_start(integer total_number)
{
llSetTimerEvent(30);
}
collision(integer numDetected)
{
if(llDetectedName(0) != previously_Welcomed)
{
previously_Welcomed=llDetectedName(0);
llSay(0,"Welcome " + llDetectedName(0));
}
}
timer()
{
previously_Welcomed = "";
}
}