#include <stdio.h>
#include <math.h>
#include <sstream>
#include <string>
#include <iostream>
#include <limits>
#include <stdexcept>
#include <unordered_set>
#include <unordered_map>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>
#include <cstdlib>
#include <numeric>
#include <array>
#include <iomanip>      // std::setprecision
#include <tuple>
#include <iostream>
#include <fstream>

using namespace std;

#define int int64_t

int32_t main() { //== Merge Equals
    /*
     https://codeforces.com/group/Ap6SQK7app/contest/309423/problem/E
     https://codeforces.com/problemset/problem/962/D
     data structures
     implementation *1600

     7
     3 4 1 2 2 1 1

     4
     3 8 2 1

     */
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    int N;
    cin >> N;
    vector<int> a(N, -1);
    map< int, set<int> > dupLists; // orderedMap === { value : { all positinos of this value, in accending order } }
    for(int i = 0; i < N; ++i) {
        int c;
        cin >> c;
        a[i] = c;
        dupLists[c].insert(i);
    }

    for( auto it = dupLists.begin(); it != dupLists.end(); ) { //== G_searched
        /*for (auto it2 = dupLists.begin(); it2 != dupLists.end(); it2++) {
            if (it == it2) {
                cerr << "-> ";
            }
            cerr << it2->first << ": ";
            for (int pos: it2->second) {
                cerr << pos << ' ';
            }
            cerr << endl;
        }
        cerr << endl;*/
        auto& lst = it->second;
        if( lst.size() > 1 ){ //== the first ( smallest ) key, who has duplictes
            int leftDupPos = *lst.begin();
            int rightDupPos = *(++lst.begin()); //== the right side of duplicate's position
            //cerr << "!!! " << leftDupPos << ' ' << rightDupPos << endl;
            lst.erase(leftDupPos);
            a[leftDupPos] = -1; //== mark a removed position
            lst.erase(rightDupPos);
            a[rightDupPos] *= 2;
            dupLists[a[rightDupPos]].insert(rightDupPos);
        } else {
            it++;
        }
    }
    //== how about output ?
    int remainTotal = 0;
    for(auto ele : a) {
        if( ele > 0 ){
            remainTotal++;
        }
    }
    cout << remainTotal << endl;
    for( auto ele : a){
        if( ele > 0 ){
            cout << ele << " ";
        }
    }

    return 0;
}