int led  = 2, buton1= 3,buton2=4; 
unsigned int sure  = 1000; 

void setup() {
  pinMode(led,OUTPUT); 
  pinMode(buton1, INPUT); 
  pinMode(buton2, INPUT); 

  
}

void loop() {  
  
 if(digitalRead(buton1)==1)
  sure -=50; 
   
 else if(digitalRead(buton2)==1)
  sure += 50; 

  digitalWrite (led,1); 
  delay(sure); 
  digitalWrite (led,0); 
  delay (sure); 

 
}