text: #include "foo/foo.h"
  
  #include <algorithm>
  #include <functional>
  #include <numeric>
  #include <vector>
  
  namespace foo 
  {
  	int factorial(int n) 
  	{
  		std::vector<int> vec(n);
  
  		std::iota(vec.begin(), vec.end(), 1);
  		return std::accumulate(vec.begin(), vec.end(), 1, 
  				std::multiplies<int>());
  	}
  }