#include <bits/stdc++.h>
using namespace std;
long long i = 0, j = 0, k = 0, cnt = 0, sum = 0, start = 0, finall = 0,
          maxi = 0, mini = 1000000007, len = 0, cnt1 = 0, cnt2 = 0, ans = 0;
int flag = 0;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  while (t--) {
    int n;
    cin >> n;
    long long a;
    set<pair<long long, long long> > s;
    for (i = 1; i <= n; i++) {
      cin >> a;
      s.insert(make_pair(a, i));
    }
    vector<pair<long long, long long> > v;
    while (true) {
      auto it = s.begin();
      auto itt = next(it, 1);
      if (s.size() == 1) {
        long long p = (*it).first;
        long long q = (*it).second;
        v.push_back(make_pair(q, p));
        s.erase(it);
        break;
      }
      if ((*it).first == (*itt).first) {
        long long p = 2 * ((*it).first);
        long long q = (*itt).second;
        s.insert(make_pair(p, q));
        s.erase(it);
        s.erase(itt);
      } else if ((*it).first != (*itt).first) {
        long long p = (*it).first;
        long long q = (*it).second;
        v.push_back(make_pair(q, p));
        s.erase(it);
      }
    }
    sort((v).begin(), (v).end());
    cout << v.size() << "\n";
    for (auto it = v.begin(); it != v.end(); it++) {
      cout << (*it).second << " ";
    }
  }
}
