#include <bits/stdc++.h>
using namespace std;
const int M = 150007;
long long n, a, wazne, tab[M], b;
map<long long, long long> m;
set<long long> s;
map<long long, set<long long> > mapa;
vector<pair<long long, long long> > v;
set<long long> s2;
int main() {
  scanf("%lld", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%lld", &tab[i]);
    if (s2.find(tab[i]) == s2.end()) s2.insert(tab[i]);
    m[tab[i]]++;
    if (m[tab[i]] >= 2 && s.find(tab[i]) == s.end()) s.insert(tab[i]);
    mapa[tab[i]].insert(i);
  }
  while (!s.empty()) {
    wazne = *s.begin();
    m[wazne] = m[wazne] - 2;
    if (m[wazne] < 2) s.erase(wazne);
    m[2 * wazne]++;
    if (s2.find(2 * wazne) == s2.end()) s2.insert(2 * wazne);
    if (m[2 * wazne] >= 2 && s.find(2 * wazne) == s.end()) s.insert(2 * wazne);
    mapa[wazne].erase(mapa[wazne].begin());
    mapa[2 * wazne].insert(*mapa[wazne].begin());
    mapa[wazne].erase(mapa[wazne].begin());
  }
  while (!s2.empty()) {
    a = *s2.begin();
    s2.erase(s2.begin());
    while (!mapa[a].empty()) {
      v.push_back(make_pair(*mapa[a].begin(), a));
      mapa[a].erase(mapa[a].begin());
    }
  }
  sort(v.begin(), v.end());
  printf("%d\n", v.size());
  for (int i = 0; i < v.size(); i++) printf("%lld ", v[i].second);
  return 0;
}
