template <typename T> T calculateSum(T a) {
  return a;
}

template <typename T> T calculateSum(T a, T b) {
  return a + b;
}

template <typename T, typename... Targs> T calculateSum(T first, Targs... rest) {
  return calculateSum(first, calculateSum(rest...));
}


template <typename T> size_t calculateCount(T a) {
  return 1;
}

template <typename T> size_t calculateCount(T a, T b) {
  return 2;
}

template <typename T, typename... Targs> size_t calculateCount(T first, Targs... rest) {
  return 1 + calculateCount(rest...);
}

template <typename T, typename... Targs> double calculateAverage(T first, Targs... rest) {
  size_t n = calculateCount(first, rest...);
  T s = calculateSum(first, rest...);
  return double(s) / n;
}

void setup() {
  int sum;
  double avg;

  Serial.begin(115200);  Serial.println();
  Serial.println(F("-------------------"));
  Serial.print(F("sum: ")); Serial.println(calculateSum(1));
  Serial.print(F("sum: ")); Serial.println(calculateSum(1, 2));
  Serial.print(F("sum: ")); Serial.println(calculateSum(1, 2, 3));
  Serial.print(F("sum: ")); Serial.println(calculateSum(1, 2, 3, 4));

  Serial.println(F("-------------------"));
  Serial.print(F("average: ")); Serial.println(calculateAverage(1, 2, 3));
  Serial.print(F("average: ")); Serial.println(calculateAverage(1, 2, 3, 4));
}

void loop() {}