//combat 

#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main()
{
  ifstream cin("balance.in");
  for (int n;cin>>n,n!=0;){
    vector<int> v(n);
    for (int i=0;i<n;i++) cin>>v[i];
    if (n%2==0){
      cout<<"no"<<endl;
      continue;
    }

    for (;;){
      if (v.size()==1){
        cout<<"yes"<<endl;
        break;
      }
      vector<int> nv;
      for (int i=v.size()-1;i>=1;i--){
        if (v[i]==v[i-1]){
          for (int j=0;j<=i-3;j++) nv.push_back(v[j]);
          nv.push_back(v[i-2]+v[i-1]);
          for (int j=i+1;j<v.size();j++) nv.push_back(v[j]);
          break;
        }
      }
      if (nv.size()==0){
        cout<<"no"<<endl;
        break;
      }
      v=nv;
    }
  }
  return 0;
}

/*

int tbl[2000][2000];
int v[2000];

int solve(int f,int t)
{
  if (f>t) return 0;
  if (f==t) return v[f];
  if (tbl[f][t]>=0) return tbl[f][t];
  int ret=0;
  for (int i=f+2;i<=t;i+=2){
    int l=solve(f+1,i-1);
    int r=solve(i,t);
    if (l>0&&r>0&&l==r){
      ret=v[f]+l;
      break;
    }
  }
  return tbl[f][t]=ret;
}

int main()
{
  ifstream cin("balance.in");
  for (int n;cin>>n,n!=0;){
    for (int i=0;i<n;i++) cin>>v[i];
    if (n%2==0){
      cout<<"no"<<endl;
      continue;
    }
    for (int i=0;i<n;i++)
      for (int j=0;j<n;j++)
        tbl[i][j]=-1;
    cout<<(solve(0,n-1)!=0?"yes":"no")<<endl;
  }
  return 0;
}

 */