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#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,b) for (int i = (a); i <= (b); ++i)
#define REPD(i,a,b) for (int i = (a); i >= (b); --i)
#define FORI(i,n) REP(i,1,n)
#define FOR(i,n) REP(i,0,int(n)-1)
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define vi vector<int>
#define ll long long
#define SZ(x) int((x).size())
#define DBG(v) cerr << #v << " = " << (v) << endl;
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define fi first
#define se second

const int N = 300300;
int a[N];

int main() {
	int n;
	scanf("%d", &n);
	FOR(i,n) {
		int x;
		scanf("%d", &x);
		a[x]++;
	}
	int mx=0;
	FOR(i,N-1) {
		a[i+1] += a[i]/2;
		if (a[i]) mx=i;
	}
	printf("%d\n", mx);
	return 0;
}