template<typename ForwardIter,
  typename OutputIter, typename UnaryPred>
OutputIter copy_if(ForwardIter begin, ForwardIter end,
  OutputIter dest, UnaryPred f) {
  while(begin != end) {
    if(f(*begin))
     *dest++ = *begin;
    ++begin;
  }

template<typename ForwardIter,
  typename OutputIter, typename UnaryPred>
OutputIter copy_if(ForwardIter begin, ForwardIter end,
  OutputIter dest, UnaryPred f) {
  while(begin != end) {
    if(f(*begin))
     *dest++ = *begin++;
    
  }