int btn=2,led1=3,led2=4,led3=5,mode=0,last=1;
void setup(){
  pinMode(btn, INPUT_PULLUP);
  pinMode(led1,OUTPUT);
  pinMode(led2, OUTPUT);pinMode(led3, OUTPUT);
}
void loop(){
  int state = digitalRead(btn);
  if(state==LOW&& last==HIGH)
  {
    mode=(mode+1)%3; delay(200);}
    last=state;
    digitalWrite(led1,mode!=2);
    digitalWrite(led2,mode==1);
    digitalWrite(led3,mode==0);
}