//GNC

#include<iostream>
#include<string>
#include <vector>
#include <algorithm>
#include <map>
#include <set>
#include <fstream>
#include <sstream>
#include <iterator>
#include <cassert>
using namespace std;
typedef vector<int> array;
//typedef set<int> seti;
typedef int seti;
//typedef pair<int,int> ipair;
//map<int, seti> table;
vector<seti> table;
seti phi;
inline int ipair(int a, int b) { return ((a<<11)+b);}

seti length(array &data, int from, int to)
{
  if ( from>=to ) return -1;//phi;
  if ( from+2==to ) return -1;//phi;
  if ( (to-from)%2==0 ) return -1;//phi;
  if ( table[ipair(from,to)]!=0 ) //table.count(ipair(from,to)) ) 
    return table[ipair(from,to)];
  seti ret=-1;
  if ( from+1==to ) {
    ret=data[from];//.insert(data[from]);
  }
  else{
    int first=data[from];
    for ( int i=from+2 ; i<to ; i+=2 ) {
      //if ( (i-(from+1))%2==0 ) continue;
      seti s1=(length(data,from+1,i));
      seti s2=(length(data,i,to));
      if ( s1>0 && s1==s2 ) {
	//assert
	ret=s1+first;
	break;
      }
      /*for ( seti::iterator it=s1.begin() ; it!=s1.end() ;
	    ++it ) {
	if ( s2.count(*it) ) ret.insert(*it+first);
	}*/
    }
  }
  table[ipair(from,to)]=ret;
  //assert(ret.size()<=1);
  return table[ipair(from,to)];
}

int main(void)
{
  int ndata;
  ifstream cin("balance.in");
  while ( cin>>ndata && ndata>0) {
    array data;
    for ( int i=0 ; i<ndata ; i++ ) {
      int a;
      cin>>a;
      data.push_back(a);
    }
    table.clear();
    table.resize(1<<22);
    cout<<(length(data,0,ndata)>=0?"yes":"no")<<endl;
    //cout<<(length(data,0,ndata).size()>0?"yes":"no")<<endl;
  }
  return 0;
}