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

#define fru(j,n) for(int j=0; j<(n); ++j)
#define tr(it,v) for(auto it=(v).begin(); it!=(v).end(); ++it)
#define x first
#define y second
#define pb push_back
#define ALL(G) (G).begin(),(G).end()

#if 1
	#define DEB printf
#else
	#define DEB(...)
#endif

typedef long long ll;
typedef long long LL;
typedef double D;
typedef pair<int,int> pii;
typedef vector<int> vi;

const int inft = 1000000009;
const int mod = 1000000007;
const int MAXN = 1000006;

int T[MAXN+4];
void solve() {
	int n;
	scanf("%d",&n);
	fru(i,n){
		int a;
		scanf("%d",&a);
		T[a]++;
	}
	int ret=0;
	fru(i,MAXN){
		if(T[i])ret=i;
		T[i+1]+=T[i]/2;
	}
	printf("%d\n",ret);
}

int main() {
	int te = 1;
//	scanf("%d",&te);
	fru(ti,te) solve();
	return 0;
}