#include <bits/stdc++.h>
const int mod = 1e9 + 7;
const int maxn = 2e5 + 6;
const double eps = 1e-6;
using namespace std;
bool eq(const double &a, const double &b) { return fabs(a - b) < eps; }
bool ls(const double &a, const double &b) { return a + eps < b; }
bool le(const double &a, const double &b) { return eq(a, b) || ls(a, b); }
long long gcd(long long a, long long b) { return a == 0 ? b : gcd(b % a, a); };
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
long long kpow(long long a, long long b) {
  long long res = 1;
  a %= mod;
  if (b < 0) return 1;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
long long read() {
  long long x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
struct P {
  long long v, x;
  bool operator<(const P &c) const { return x < c.x; }
} ans[maxn];
map<long long, long long> m;
priority_queue<pair<long long, long long>, vector<pair<long long, long long> >,
               greater<pair<long long, long long> > >
    q;
int main() {
  int n;
  long long x;
  scanf("%d", &n);
  m.clear();
  for (int i = 1; i < (n + 1); ++i) {
    scanf("%lld", &x);
    m[x]++;
    q.push(make_pair(x, (long long)i));
  }
  int cnt = 0;
  while (q.size()) {
    pair<long long, long long> t = q.top();
    q.pop();
    if (m[t.first] < 2) {
      ans[cnt].v = t.first;
      ans[cnt++].x = t.second;
      continue;
    }
    pair<long long, long long> t1 = q.top();
    q.pop();
    m[t1.first] -= 2;
    m[t.first + t1.first]++;
    q.push(make_pair(t.first + t1.first, max(t.second, t1.second)));
  }
  sort(ans, ans + cnt);
  printf("%d\n", cnt);
  for (int i = 0; i < (cnt); ++i)
    printf("%lld%c", ans[i].v, " \n"[i == cnt - 1]);
  return 0;
}
