#include<bits/stdc++.h>
using namespace std;
#define int long long 
int n,a[100100];
int ans;
int c[100100][31];
int f[100100][31];
signed main(){
	cin>>n;
	for (int i=1;i<=n;i++)
	cin>>a[i];
	ans=n;
	for (int i=1;i<n;i++){
		int x=a[i+1]-a[i]-1;
		for (int j=0;j<=30;j++)
		if(x>(1ll<<j))c[i][j]=1ll<<j,x-=1ll<<j;
		else {c[i][j]=x;break;}
//		for (int j=0;j<=4;j++)
//		cout<<i<<" "<<j<<" "<<c[i][j]<<"\n"; 
	}
	for (int i=1;i<n;i++){
		for (int j=0;j<=30;j++){
			f[i][j]=i-1+c[i][j]+1;
			for (int k=0;k<=j;k++)
			f[i][j]=max(f[i][j],f[i-1][k]+c[i][j]+(j>k)); 
		}
	}
	for (int j=0;j<=30;j++)
	ans=max(ans,f[n-1][j]);
	cout<<ans<<"\n";
}