#include 

int spawn(int n, tf::Subflow& sbf) {
  if (n < 2) return n;
  int res1, res2;

  // compute f(n-1)
  sbf.emplace([&res1, n] (tf::Subflow& sbf) { res1 = spawn(n - 1, sbf); } )
     .name(std::to_string(n-1));

  // compute f(n-2)
  sbf.emplace([&res2, n] (tf::Subflow& sbf) { res2 = spawn(n - 2, sbf); } )
     .name(std::to_string(n-2));

  sbf.join();
  return res1 + res2;
}

int main(int argc, char* argv[]) {

  if(argc != 2) {
    std::cerr