invalid conversion from 'int' to 'void'

This is my code after editing, i have change the int to void for the rpm

void rpm()   //integer function that can store between -32768 and 32767.

this is my full code

#include <Servo.h>

Servo myservo;
volatile int NbTopsFan; //measuring the rising edges of the signal
int Calc;  
int potPin = 0; //analog pin ued to connect the sensor
int ledPin = 9;  //select pin for the servo
int val = 0;  //variable to read the value from the analog pin
void rpm()   //integer function that can store between -32768 and 32767.

{
  NbTopsFan++;  //This function measures the rising and falling edge of the 
}
{
  myservo.attach(9); //set up the servo as usual

  pinMode(ledPin, OUTPUT);  //variable to store the value coming from the sensor
  pinMode(potPin, INPUT); //initializes digital pin 0 as an input
  Serial.begin(9600); //for watching the speeds in the serial monitor
  attachInterrupt(0, rpm, RISING); //and the interrupt is attached
}
void loop()
{
  NbTopsFan = 0;      //Set NbTops to 0 ready for calculations
  sei();            //Enables interrupts
  val = analogRead(potPin);    // read the value from the sensor
  val = map(val,0,1023,0,179);
  cli();            //Disable interrupts
  Calc = (NbTopsFan * 60 / 7.5); //(Pulse frequency x 60) / 7.5Q, = flow rate 
   
   if (val>79) myservo.writeMicroseconds(0);  //set servo to mid-point
  
   else if (val<80) myservo.writeMicroseconds(1500);  
 
  Serial.print (Calc, DEC); //Prints the number calculated above
  Serial.print (" L/hour\r\n"); //Prints "L/hour" and returns a  new line
  Serial.println(val);
 delay(10); 

}

BUT I still got this error message at this line,

{
  NbTopsFan++;  //This function measures the rising and falling edge of the 
}
{

it says
sketch_may03a:14: error: expected unqualified-id before '{' token

hmm...how do i fix this error?