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#include <bits/stdc++.h>
#include <unordered_map>
using namespace std;
#define PB push_back
#define MP make_pair
#define LL long long
#define int LL
#define FOR(i,a,b) for(int i = (a); i <= (b); i++)
#define FORD(i,a,b) for(int i = (a); i >= (b); i--)
#define RE(i,n) FOR(i,1,n)
#define REP(i,n) FOR(i,0,(int)(n)-1)
#define R(i,n) REP(i,n)
#define VI vector<int>
#define PII pair<int,int>
#define LD long double
#define FI first
#define SE second
#define st FI
#define nd SE
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define M_PI 3.14159265358979323846
template<class C> void mini(C& _a4, C _b4) { _a4 = min(_a4, _b4); }
template<class C> void maxi(C& _a4, C _b4) { _a4 = max(_a4, _b4); }

template<class TH> void _dbg(const char *sdbg, TH h) { cerr << sdbg << '=' << h << endl; }
template<class TH, class... TA> void _dbg(const char *sdbg, TH h, TA... a) {
	while (*sdbg != ',')cerr << *sdbg++; cerr << '=' << h << ','; _dbg(sdbg + 1, a...);
}

template<class T> ostream& operator<<(ostream& os, vector<T> V) {
	os << "["; for (auto& vv : V) os << vv << ","; os << "]";
	return os;
}

template<class T> ostream& operator<<(ostream& os, set<T> V) {
	os << "["; for (auto& vv : V) os << vv << ","; os << "]";
	return os;
}

template<class L, class R> ostream &operator<<(ostream &os, pair<L, R> P) {
	return os << "(" << P.st << "," << P.nd << ")";
}


#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (__VA_ARGS__)
#endif

int32_t main(int32_t argc, char ** argv) {
	ios_base::sync_with_stdio(0);
	VI inp((int)3e5);
	int n;
	cin >> n;
	REP(i, n) {
		int t;
		cin >> t;
		inp[t]++;
	}
	REP(i, SZ(inp) - 1) {
		inp[i + 1] += inp[i] / 2;
	}
	FORD(i, SZ(inp) - 1, 0) {
		if (inp[i]) {
			cout << i << "\n";
			return 0;
		}
	}
}