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#include <cstdio>
#include <cstring>
#include <cmath>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <iterator>
#include <string>
#include <vector>
#include <queue>
#include <bitset>
#include <utility>
#include <stack>

using namespace std;
typedef long long LL;
typedef pair<int,int> PII;
typedef vector<int> VI;
#define MP make_pair
#define FOR(v,p,k) for(int v=(p);v<=(k);++v)
#define FORD(v,p,k) for(int v=(p);v>=(k);--v)
#define REP(i,n) for(int i=0;i<(n);++i)
#define VAR(v,i) __typeof(i) v=(i)
#define FOREACH(i,c) for(VAR(i,(c).begin());i!=(c).end();++i)
#define PB push_back
#define ST first
#define ND second
#define SIZE(x) (int)x.size()
#define ALL(c) c.begin(),c.end()

#define ODD(x) ((x)%2)
#define EVEN(x) (!(ODD(x)))

int main() {
    int max_exp = 201718+100; //+ log(max_n)
    VI coeff(max_exp);

    int n;
    scanf("%d", &n);
    REP(i, n) {
        int a;
        scanf("%d", &a);
        coeff[a]++;
    }
    int best = 0;
    int curr_coeff = 0;
    REP(i, coeff.size()) {
        curr_coeff += coeff[i];
        if (curr_coeff > 0) best=i;
        curr_coeff /= 2;
    }
    printf("%d\n", best);
    return 0;
}