int p1=13; 
int p2=7; 
int p3=8; 
void setup() 
{ 
 // put your setup code here, to run once: 
 pinMode(p1, OUTPUT); 
 pinMode(p2, INPUT); 
 pinMode(p3, OUTPUT); 
}
void loop() 
{ 
 // put your main code here, to run repeatedly: 
 if(digitalRead(p2)==0) 
 { 
  digitalWrite(p1, LOW); digitalWrite(p3, HIGH); 
 delay(500); 
 } 
else 
 { 
 digitalWrite(p1, HIGH); 
 digitalWrite(p3, LOW); 
 } 
}