#include<iostream>
#include<list>
using namespace std;

int main(){
   list<int> l{1,2,3,4,5};
   l.push_back(6);
   l.push_back(7);
   //prosthetei sto telos listas

   l.push_front(8);
   l.push_front(9);

   for (list<int>::iterator p=l.begin(); p!=l.end();p++) {
      cout<<*p<<endl;
   }
   l.pop_back();
   cout<< l.back() <<endl;
   int sum=0;
   while(!l.empty() ) {
      sum+=l.front();
      l.pop_front();
   }
   cout<<"SUM="<<sum<<endl;
return 0;
}