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

int n,a[100001];
int F[64],top;

signed main(){
ios::sync_with_stdio(false),cin.tie(0);

cin>>n;
for (int i=1;i<=n;++i) cin>>a[i];

int ans=n;

for (int i=n;i>1;--i){
int len=a[i]-a[i-1]-1;
top=0;
int g=(len==0?0:1+__lg(len));
for (int k=g-1;k>=1;--k) F[k]+=(1ll<<(k-1));
if (g>1) F[g-1]=max(F[g-1],F[g]+max((1ll<<(g-2))+1,min(1ll<<(g-1),len-(1ll<<(g-1))+2)));
F[g]+=min(1ll<<(g-1),len-(1ll<<(g-1))+1);
for (int k=62;k;--k) F[k]=max(F[k],F[k+1]);
ans=max(ans,F[1]+i-1);
}

cout<<ans<<'\n';

return 0;
}