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

namespace FastIO
{
	class FastIOBase
	{
	protected:
#ifdef OPENIOBUF
		static const int BUFSIZE=1<<22;
		char buf[BUFSIZE+1];
		int buf_p=0;
#endif
		FILE *target;
	public:
#ifdef OPENIOBUF
		virtual void flush()=0;
#endif
		FastIOBase(FILE *f): target(f){}
		~FastIOBase()=default;
	};

	class FastOutput: public FastIOBase
	{
#ifdef OPENIOBUF
	public:
		inline void flush()
			{ fwrite(buf,1,buf_p,target),buf_p=0; }
#endif
	protected:
		inline void __putc(char x)
		{
#ifdef OPENIOBUF
			if(buf[buf_p++]=x,buf_p==BUFSIZE)flush();
#else
			putc(x,target);
#endif
		}
		template<typename T>
		inline void __write(T x)
		{
			static char stk[64],*top;top=stk;
			if(x<0) return __putc('-'),__write(-x);
			do *(top++)=x%10,x/=10; while(x);
			for(;top!=stk;__putc(*(--top)+'0'));
		}
	public:
		FastOutput(FILE *f=stdout): FastIOBase(f){}
#ifdef OPENIOBUF
		~FastOutput(){ flush(); }
#endif
		template<typename ...T>
		inline void writesp(const T &...x)
			{ initializer_list<int>{(this->operator<<(x),__putc(' '),0)...}; }
		template<typename ...T>
		inline void writeln(const T &...x)
			{ initializer_list<int>{(this->operator<<(x),__putc('\n'),0)...}; }
		inline FastOutput &operator <<(char x)
			{ return __putc(x),*this; }
		inline FastOutput &operator <<(const char *s)
			{ for(;*s;__putc(*(s++)));return *this; }
		inline FastOutput &operator <<(const string &s)
			{ return (*this)<<s.c_str(); }
		template<typename T,typename=typename enable_if<is_integral<T>::value>::type>
		inline FastOutput &operator <<(const T &x)
			{ return __write(x),*this; }
	}qout;

	class FastInput: public FastIOBase
	{
#ifdef OPENIOBUF
	public:
		inline void flush()
			{ buf[fread(buf,1,BUFSIZE,target)]='\0',buf_p=0; }
#endif
	protected:
		inline char __getc()
		{
#ifdef OPENIOBUF
			if(buf_p==BUFSIZE) flush();
			return buf[buf_p++];
#else
			return getc(target);
#endif
		}
	public:
#ifdef OPENIOBUF
		FastInput(FILE *f=stdin): FastIOBase(f){ buf_p=BUFSIZE; }
#else
		FastInput(FILE *f=stdin): FastIOBase(f){}
#endif
		inline char getchar() { return __getc(); }
		template<typename ...T>
		inline void read(T &...x)
			{ initializer_list<int>{(this->operator>>(x),0)...}; }
		inline FastInput &operator >>(char &x)
			{ while(isspace(x=__getc()));return *this; }
		template<typename T,typename=typename enable_if<is_integral<T>::value>::type>
		inline FastInput &operator >>(T &x)
		{
			static char ch,sym;x=sym=0;
			while(isspace(ch=__getc()));
			if(ch=='-') sym=1,ch=__getc();
			for(;isdigit(ch);x=(x<<1)+(x<<3)+(ch^48),ch=__getc());
			return sym?x=-x:x,*this;
		}
		inline FastInput &operator >>(char *s)
		{
			while(isspace(*s=__getc()));
			for(;!isspace(*s) && *s && ~*s;*(++s)=__getc());
			return *s='\0',*this;
		}
		inline FastInput &operator >>(string &s)
		{
			char str_buf[(1<<8)+1],*p=str_buf;
			char *const buf_end=str_buf+(1<<8);
			while(isspace(*p=__getc()));
			for(s.clear(),p++;;p=str_buf)
			{
				for(;p!=buf_end && !isspace(*p=__getc()) && *p && ~*p;p++);
				*p='\0',s.append(str_buf);
				if(p!=buf_end) break;
			}
			return *this;
		}
	}qin;
}
using namespace FastIO;

typedef long long LL;
typedef long double LD;
typedef unsigned int UI;
typedef unsigned long long ULL;

#ifndef DADALZY
#define FILEIO(file) freopen(file".in","r",stdin),freopen(file".out","w",stdout)
#else
#define FILEIO(file)
#endif

LL n,m,a[100005],dp[100005][65];
int main()
{
	qin>>n;
	for(int i=1;i<=n;i++) qin>>a[i];
	for(int i=2;i<=n;i++) m=max(m,(LL)log2(a[i]-a[i-1]-1)+1);
	for(int i=0;i<=m;i++) dp[1][i]=1;
	for(int i=2;i<=n;i++)
	{
		int c=log2(a[i]-a[i-1]-1)+1;
		dp[i][0]=dp[i-1][0]+1;
		for(int j=1;j<=c;j++)
		{
			LL x=(j!=c)?(1ll<<(j-1)):(a[i]-a[i-1]-(1ll<<(j-1)));
			dp[i][j]=dp[i-1][j]+x;
			if(j==c && x!=(1ll<<(j-1))) dp[i][j]=max(dp[i][j],dp[i-1][j-1]+max(1ll<<(j-2),x)+1);
			dp[i][j]=max({dp[i][j],dp[i-1][j],dp[i][j-1]});
		}
		for(int j=c+1;j<=m;j++) dp[i][j]=max(dp[i-1][j],dp[i][j-1]);
	}
	qout<<dp[n][m];
	return 0;
}