#include <bits/stdc++.h>
using namespace std;
ifstream fin("test.in");
void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
template <typename T, typename V>
void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T>
void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x) cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V>
void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v)) cerr << ", ";
  _print(v...);
}
void debug3(int *t, int st, int n) {
  cerr << '{' << t[st];
  for (int i = st + 1; i <= n; i++) cerr << ",", __print(t[i]);
  cerr << "}" << '\n';
}
int v[200005];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n, i, x, p;
  cin >> n;
  p = 0;
  for (i = 1; i <= n; i++) {
    cin >> x;
    while (v[p] == x) {
      x++;
      p--;
    }
    p++;
    v[p] = x;
  }
  cout << p << '\n';
  for (i = 1; i <= p; i++) cout << v[i] << " ";
}
