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#include<iostream>
#include<assert.h>
#include<cstdio>
#include<string>
#include<cmath>
#include<bitset>
#include<vector>
#include<map>
#include<set>
#include<algorithm>
#include<utility>
using namespace std;

#define FOR(I,A,B) for(int I=(A);I<=(B);I++)
#define REP(I,N) for(int I=0;I<(N);I++)
#define ALL(X) (X).begin(),(X).end()
#define PB push_back
#define MP make_pair
#define f first
#define s second

//#define DEBUG true
#ifdef DEBUG
#define SHOW(NAME, VAL) cout << NAME << ": " << VAL << '\n'
#else
#define SHOW(NAME, VAL)
#endif

typedef vector<int> VI;
typedef pair<int,int> PII;
typedef long long ll;
typedef vector<string> VS;

constexpr int maxDenom = 201718;
int coins[maxDenom + 2];

void test() {
	// initialize
	FOR(i, 0, maxDenom) {
		coins[i] = 0;
	}

	// read input
	int n;
	cin >> n;
	REP(i, n) {
		int a;
		cin >> a;
		coins[a]++;
	}

	// propagate
	FOR(i, 0, maxDenom) {
		coins[i + 1] += coins[i] / 2;
		coins[i] %= 2;
	}

	// find max
	int highestDenom = 0;
	FOR(i, 0, maxDenom + 1) {
		if(coins[i] > 0) {
			highestDenom = i;
		}
	}
	
	int coinsCount = coins[highestDenom];
	while(coinsCount >= 2) {
		highestDenom++;
		coinsCount /= 2;
	}

	cout << highestDenom << '\n';
}

int main() {
	std::ios_base::sync_with_stdio(false);
	int t;
	t = 1;
	// cin >> t;
	FOR(i, 1, t) {
		test();
	}
	return 0;
}