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#include <bits/stdc++.h>
// #pragma GCC optimize ("O3")
// #pragma GCC target ("sse4")
using namespace std;

typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int,int> PII;

#define REP(i,n) for(int i=0;i<(n);++i)
#define FOR(i,a,b) for (int i=(a); i<(b); ++i)
#define FORD(i,a,b) for (int i=(a)-1; i>=(b); --i)

#define pb push_back
#define mp make_pair
#define st first
#define nd second

const int MOD = 1000000007;

int T[250000];
int main() {
  // ios_base::sync_with_stdio(0);

  int N;
  scanf("%d", &N);
  REP(i,N) {
    int a;
    scanf("%d", &a);
    ++T[a];
  }
  int result = 0;
  REP(i,210000) {
    if (T[i] > 0) result = i;
    T[i+1] += T[i] / 2;
  }
  printf("%d\n", result);
}