// Task: a.cc
// Created at Mon, Nov 20, 2017  4:13:24 PM

#include <bits/stdc++.h>
using namespace std;

namespace {
    struct point_t;
    using i64 = int64_t;
    using u64 = uint64_t;
    #define all(x) begin(x),end(x)
    template<typename T = int> T read();
    template<typename T = int> vector<T> read_vec(size_t const n);
    template<typename T>ostream& operator<<(ostream& os, vector<T> const vec);
    template<typename T> T gcd(T const a, T const b);
}

u64 highest_pow(u64 x) {
    for(int i=31; i>=0; --i) {
        if(x & (1 << i)) return i;
    }
    return 0;
}

int main(int, char**) {
    // cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    constexpr int MAXIMUM = 201718;
    auto a = read_vec<i64>(read());
    vector<int> freq(MAXIMUM + 1, 0);
    for_each(all(a), [&](int x) {++freq[x]; });

    i64 maxNonZero = [&](){
        int res = 0;
        for(size_t i=0; i<freq.size()-1; ++i) {
            freq[i+1] += freq[i] / 2;
            freq[i] = freq[i] % 2;
            if(freq[i]) res = i;
        }
        return res;
    }();

    cout << (freq[MAXIMUM] ? MAXIMUM + highest_pow(freq[MAXIMUM]) : maxNonZero) << '\n';
}

/**************************************************************************************************
 ********************************* DEFINITIONS OF HELPER FUNCTIONS ********************************
 **************************************************************************************************/

namespace {
    template<typename T = int>
    T read() { T x; cin >> x; return x; }

    template<typename T = int>
    vector<T> read_vec(size_t const n) {
        vector<T> vec(n);
        copy_n(istream_iterator<T>(cin), n, begin(vec));
        return vec;
    }

    template<typename T>
    ostream& operator<<(ostream& os, vector<T> const vec) {
        copy(begin(vec), end(vec), ostream_iterator<T>(os, " "));
        return os;
    }

    template<typename T>
    T gcd(T const a, T const b) { return a==0 ? b : gcd(b%a, a); }

    struct point_t {
        int x, y;
        point_t(int _x, int _y) : x{_x}, y{_y} {}
        friend istream& operator>>(istream& is, point_t& p) { is>>p.x>>p.y; return is; }
    };
}