#include <bits/stdc++.h>
using namespace std;
int main() {
  long long c[150000];
  for (int i = 0; i < 150000; i++) c[i] = -1;
  int n;
  cin >> n;
  map<long long, vector<int> > m;
  set<long long> a;
  for (int i = 0; i < n; i++) {
    long long k;
    cin >> k;
    a.insert(k);
    m[k].push_back(i);
  }
  set<long long>::iterator it;
  it = a.begin();
  while (it != a.end()) {
    long long t = *it;
    sort(m[t].begin(), m[t].end());
    for (int i = 0; i < m[t].size(); i++) {
      if (i % 2 == 1) {
        m[2 * t].push_back(m[t][i]);
        a.insert(2 * t);
        n--;
      }
    }
    if (m[t].size() % 2 == 1) c[m[t][m[t].size() - 1]] = t;
    a.erase(t);
    it = a.begin();
  }
  cout << n << "\n";
  for (int i = 0; i < 150000; i++) {
    if (c[i] != -1) cout << c[i] << " ";
  }
}
