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#include<bits/stdc++.h>
#define rep(i,k,n) for(ll i= (ll) k;i< (ll) n;i++)
#define all(v) (v).begin(), (v).end()
#define SZ(v) (int)((v).size())
#define pb push_back
#define ft first
#define sd second
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
const long long INF = 1e18L + 1;
const int IINF = 1e9 + 1;

using namespace std;

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...);
}

#ifdef LOCAL
#define DBG(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#else
#define DBG(...) (__VA_ARGS__)
#define cerr if(0)cout
#endif

const int N = 300000;

int main() {
#ifndef LOCAL
    ios_base::sync_with_stdio(0);
    cin.tie(0);
#endif
  
	int n;
	cin >> n;
	vector<int> a(N + 1);
	rep (i, 0, n) {
		int x;
		cin >> x;
		a[x]++;
	}
	rep (i, 0, N) {
		a[i + 1] += a[i] / 2;
	}
	int b = 0;
	rep (i, 0, N) {
		if (a[i]) {
			b = i;
		}
	}
	cout << b;
	
    return 0;
}