#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  vector<long long> a(n);
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  set<pair<long long, int>> all;
  for (int i = 0; i < n; i++) {
    all.insert({a[i], i});
  }
  vector<pair<long long, int>> res;
  while (!all.empty()) {
    pair<long long, int> prev = *all.begin();
    all.erase(all.begin());
    if (all.empty()) {
      res.push_back(prev);
      break;
    }
    pair<long long, int> next = *all.begin();
    all.erase(all.begin());
    if (next.first != prev.first) {
      res.push_back(prev);
      all.insert(next);
    } else {
      all.insert({prev.first * 2LL, next.second});
    }
  }
  sort(res.begin(), res.end(),
       [&](pair<long long, int> a, pair<long long, int> b) {
         return a.second < b.second;
       });
  cout << res.size() << "\n";
  for (auto p : res) {
    cout << p.first << " ";
  }
  cout << "\n";
  return;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  int t = 1;
  for (int i = 1; i <= t; i++) {
    solve();
  }
  return 0;
}
