#include <bits/stdc++.h>
using namespace std;
const int maxn = 5e5 + 10;
int n;
int a[maxn];
string answer;
void f(char c) {
  int idx = -1;
  for (int i = 1; i <= n; i++)
    if (a[i] > 0) idx = i;
  if (idx == -1) return;
  for (int j = 1; j <= idx; j++) {
    answer += c;
    a[j] -= idx - j + 1;
  }
  if (c == 'a')
    f('b');
  else
    f('a');
}
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  f('a');
  cout << answer << endl;
}
