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#include <bits/stdc++.h>
using namespace std;
#define mp make_pair
#define pb push_back
#define ppb pop_back
#define eb emplace_back
#define e1 first
#define e2 second
#define For(a, b, i) for(int i=a;i<b; ++i)
#define Dfor(a, b, i) for(int i=a;i>=b; --i)
typedef long long int ll;
typedef unsigned long long int ull;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<pii, pii> pp;
const int mod=1e9+7;
const int inf=1e9+9;
const int mod69=1e9+696969;
#define maxn 1000010
ll t[maxn], n, k[maxn];
int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cin >> n;
	ll WYN = 0;
	For(0, n, i) cin >> t[i], k[t[i]]++;
	For(0, maxn, i) k[i + 1] += k[i]/2;
	For(0, maxn, i) if(k[i]) WYN = i;
	cout << WYN << "\n";
}