void setup() 
{
    Serial.begin(9600);
}

void loop() 
{
    Serial.print("Enter the first number:  ");
    while (!Serial.available())
    {
      delay(1);
    }

    int num1 = Serial.readStringUntil('\r').toInt();

    Serial.print("Enter the second Number: ");
    while (!Serial.available())
    {
      delay(1);
    }

    int num2 = Serial.readStringUntil('\r').toInt();

    int sum = num1 + num2;
    Serial.println(String(num1) + " + " + num2 + " = " + sum);
}