#include <functional>
using namespace std;
using namespace std::placeholders;

int f1(int u)
{
  return u + 7;
}

int f2(int u)
{
  return u + 13;
}

int main()
{
  auto F = bind(plus<int>(), bind(f1, _1), bind(f2, _1));
  int r = F(3);
}