#include <bits/stdc++.h>
using namespace std;
int comp(long long from, long long to) {
  vector<long long> f;
  vector<long long> t;
  while (from != 0) {
    f.push_back(from % 10);
    from /= 10;
  }
  while (to != 0) {
    t.push_back(to % 10);
    to /= 10;
  }
  if (t.size() > f.size()) return -1;
  int i = 0;
  int j = 0;
  while (i < t.size() && j < f.size()) {
    while (j < f.size() && t[i] != f[j]) {
      j++;
    }
    if (j == f.size()) return -1;
    i++;
    j++;
  }
  if (i != t.size()) return -1;
  return f.size() - t.size();
}
int main() {
  int n;
  cin >> n;
  long long a[n];
  long long oute[n];
  set<pair<long long, int> > sete;
  for (int i = 0; i < n; i++) {
    scanf("%I64d", &a[i]);
    sete.insert(make_pair(a[i], i));
    oute[i] = 0;
  }
  pair<long long, int> prev;
  prev.first = -1;
  while (!sete.empty()) {
    if (prev.first == -1) {
      pair<long long, int> p = *sete.begin();
      sete.erase(sete.begin());
      prev = p;
    } else {
      pair<long long, int> p = *sete.begin();
      sete.erase(sete.begin());
      if (prev.first == p.first) {
        oute[prev.second] = -1;
        p.first = p.first * 2;
        sete.insert(p);
        prev = *sete.begin();
        sete.erase(sete.begin());
      } else {
        oute[prev.second] = prev.first;
        prev = p;
      }
    }
  }
  if (prev.first != -1) {
    oute[prev.second] = prev.first;
  }
  int tem = 0;
  for (int i = 0; i < n; i++) {
    if (oute[i] != -1) {
      tem++;
    }
  }
  cout << tem << "\n";
  for (int i = 0; i < n; i++) {
    if (oute[i] != -1) {
      printf("%I64d ", oute[i]);
    }
  }
  return 0;
}
