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#include <bits/stdc++.h>
using namespace std;
#define int long long
int T[201800];
main (){
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  int maxa = 0;
  for (int i = 0; i < n; ++i){
    int a;
    cin >> a;
    maxa = max(maxa, a);
    T[a]++;
  }
  int j = 0;
  for (;j < maxa; ++j){
    T[j + 1] += T[j]/2;
  }
  int b = T[j];
  while (b){
    b /= 2;
    ++j;
  }
  cout << j - 1 << endl;
}