//树的深度

import java.util.*;

public class Main{

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner cin=new Scanner(System.in);
          int[] nn= new int[1001];
          int i=0;
          int n=0; 
          int count = cin.nextInt();
          nn[i++] = count;
       while((count--)!=0)
        {
            n=cin.nextInt();
            nn[i++]=n;
        }
          getlength(nn,i);
    }
      
    public static void getlength(int[] nn,int i){
          int number = i-1;
          if(number==0){System.out.print(0);return;}
          else if(number==1){System.out.print(1);return;}
          else if(number>1&&number<5){System.out.print(2);return;}
          int start = 1;
          int censhu = 0;
          censhu = number/2;
          int hehe[][] = new int[censhu][2];
          for(int i1=0;i1<censhu;i1++){
                for(int j1=0;j1<2;j1++){
                      hehe[i1][j1] = nn[start];
                      start++;
                }
          }
          int maxlength1 = 2;
          for(int i2=0;i2<censhu-1;i2++){
                for(int j2=i2+1;j2<censhu;j2++){
                      if(hehe[i2][1]==hehe[j2][0]){
                            maxlength1++;
                            i2 = j2;
                      }
                }
          }
          int maxlength2 = 2;
          for(int i3=1;i3<censhu-1;i3++){
                for(int j3=i3+1;j3<censhu;j3++){
                      if(hehe[i3][1]==hehe[j3][0]){
                            maxlength2++;
                            i3 = j3;
                      }
                }
          }
          int maxlength = 0;
          if(maxlength1>maxlength2){
                maxlength = maxlength1;
          }else{
                maxlength = maxlength2;
          }
          System.out.print(maxlength);
    }
      
}