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#include <iostream>
using namespace std;
#define fori(i, k, n) for(int i = (int)k; i < n; ++i)
int A[300000];

int main(){
  int n, a, maks = 0;
  cin>>n;
  fori(i, 0, n){
    cin>>a;
    A[a]++;
    maks = max(a, maks);
  }
  int k = 0;
  while(true){
    if(k > maks && A[k] == 0){
      k--;
      break;
    }
    else{
      A[k+1] += A[k]/2;
      k++;
    }
  }
  cout<<k<<endl;
  
}