#include<bits/stdc++.h>
using namespace std;
#define int long long 
int n,a[100100];
int ans;
int c[100100][61];
int f[100100][61];
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<=60;j++)
		if(x>(1ll<<j))c[i][j]=1ll<<j,x-=1ll<<j;
		else{ 
			c[i][j]=x;
			break;
		}
	}
	memset(f,-63,sizeof(f));
	f[0][0]=1;
	for (int i=1;i<n;i++){
		for (int j=0;j<=60;j++){
			if(c[i][j]==0)break;
			f[i][j]=f[i-1][j];
			if(c[i][j]!=(1ll<<j)){
				f[i][j]=max(f[i][j],f[i-1][j]+c[i][j]);
				int tmp=max(1ll<<j-1,c[i][j])+1;
				for (int k=0;k<j;k++)
				f[i][j]=max(f[i][j],f[i-1][k]+tmp); 
			}else{
				for (int k=0;k<=j;k++)
				f[i][j]=max(f[i][j],f[i-1][k]+c[i][j]); 
			}
		}
	}
	for (int j=0;j<=60;j++)
	ans=max(ans,f[n-1][j]);
	cout<<ans<<"\n";
}