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#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <cstdlib>
#include <vector>
#include <algorithm>
#include <cstring>
#include <string>
#include <map>
#include <deque>
using namespace std;

typedef long long LL;
typedef pair<int,int> PI;
typedef vector<int> VI;
#define ALL(a) (a).begin(),(a).end()
#define PB push_back
#define MP make_pair
#define FT first
#define SD second
#define Y first
#define X second

vector<string>token(string a) {
    vector<string>w;a.push_back(' ');
    while(!a.empty()){w.push_back(a.substr(0,a.find(" ")));a=a.substr(a.find(" ")+1,a.size()-1);}return w;
}

map<string,int> mapik;
vector<string> amapik;
int dodaj(string a) {if(mapik.count(a)==0) {mapik[a]=mapik.size()-1;amapik.PB(a);}return mapik[a];}

const int INF = 1000000000;
const LL INFINF = 1000000000000000000LL;

PI moves4[4] = { MP(1, 0), MP(-1, 0), MP(0, 1), MP(0, -1) };
PI move(PI st, PI m)
{
    return MP(st.first + m.first, st.second + m.second);
}

int rows, cols;
bool on_board(PI p)
{
    return p.first >= 0 && p.second >= 0 && p.first < rows && p.second < cols;
}

char tmp_str[1000];
string scanf_string() {
	scanf("%s",tmp_str);
	return tmp_str;
}

inline bool get_bit(int w, int i) {
	return (w>>i)&1;
}

// ==========================================================

const int N = 1000000;
int n;
int counts[N];

int main() {
	scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
        int tmp; scanf("%d",&tmp);
        counts[tmp]++;
    }
    int res = 0;
    for(int i=0;i<N;i++)
    {
        if(counts[i] > 0)
            res = i;
        counts[i+1] += counts[i] / 2;
    }
    printf("%d\n",res);
	return 0;
}