#include <Servo.h>

Servo servo;
int bf = 3;
int bb = 4;
int i = 90;

void setup() {

pinMode(bf, INPUT);
pinMode(bb, INPUT);
Serial.begin(9600);
servo.attach(9);
servo.write(90);
}

void loop() {

if (digitalRead(bf) == HIGH){  
  servo.write(i);
  delay(15);
  Serial.print("servo angle: ");
  Serial.println(i);
  i++;
  delay(25);
 if (i>180){
    i=180;
    Serial.println(i);
    }
}
else if (digitalRead(bb) == HIGH){  
  servo.write(i);
  delay(15);
  Serial.print("servo angle: ");
  Serial.println(i);
  i--;
  delay(25);
  if(i<0){
    i=0;
    Serial.println(i);
    }
}
}