i1 = GetIntFromStack(); //Particle UID 
			stack.Push(new Data(p.position.x)); 
			stack.Push(new Data(p.position.y)); 
		} else { 
			stack.Push(new Data(-1)); 
			stack.Push(new Data(-1)); 
 

	
<-particleid GetParticlePosition  ->Yp ->Xp