#include <iostream>

 #include <map>

 #include <algorithm>

 #include <set>

 #define N 150005

 using namespace std;

 typedef long long Int;

 const int maxn = 1e9 + ;

 map<long long, set<int> > mapp;

 long long a[N];

 int main()

 {

     int n;

     cin >> n;

     int all = n;

     for (int i = ; i <= n; i++)

     {

         cin >> a[i];

         mapp[a[i]].insert(i);

     }

     for (map<long long, set<int> >::iterator i = mapp.begin(); i != mapp.end(); i++)

     {

         while (i->second.size() > )

         {

             set<int>::iterator op1 = i->second.begin(), op2;

             op2 = op1; op2++;

             all--;

             int t1 = *op1, t2 = *op2;

             a[t1] = -;

             a[t2] *= ;

             mapp[a[t2]].insert(t2);

             i->second.erase(op1);

             i->second.erase(op2);

         }

     }

     cout << all << endl;

     for (int i = ; i <= n; i++)

     {

         if (a[i] != -)

             cout << a[i] << " ";

     }

     //system("pause");

     return ;

 }