#include<iostream>
using namespace std;

int main()
{
    long int i,j,tm,n,tot=0,tots=0,req=0,reqs=0,cnt=0;
    long int *a;
    long int max = 0;
    
    cin>>n;
    a = (long int *)malloc(sizeof(long int) * n);
    
    for(i=0;i<n;i++)
         cin>>a[i]; 
         
    for(i=0;i<n;i++)
        {
         tm = a[i];
         cnt = 0;
         tot = 0;
         tots = 0;
         
         for(j=i;j<n;j++)
          {
           if(a[j] > tm)
              tm = a[j];
              
           req = tm *(tm + 1) /2;
           reqs = tm *(tm + 1)*((2* tm) + 1) /6;
           
           cout<<" --------------------- REQ 1s :"<< req << " 2s :"<< reqs <<endl;
           cnt++;
           
           tot+= a[j];
           tots += (a[j] * a[j]);          
           cout<<" --------------------- TOT 1s : "<< tot << " 2s : "<< tots <<endl;           
           
           if(cnt == tm)
             {
              if(tot == req && tots == reqs)
                {
                 cout<<":::: Equal.. "<<endl;                           
                 if(cnt > max) 
                   max = cnt;
                }
              else
                   break;
             }          
          }
        }
    cout<<"MAX :: "<<max<<endl;
    getchar();
        getchar();
        
    return 0;
}