#include <fstream>
#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
#define ForU(i,a,b) for(int i=a;i<=b;i++)
#define ForD(i,a,b) for(int i=a;i>=b;i--)
int const test=0;
int const nmax=100009;
int a[nmax], b[nmax], save[nmax],
 f[nmax], rr[nmax], next[nmax], last[nmax];
int n,m;
int find(int x){
    if (x==save[1]) return 1;
    if (x==save[m]) return m;
    int l=1, r=m, t=0;
    while (r-l>1) {
          t=(l+r)/2;
          if (save[t]>x) r=t;
          else l=t;
    }
    if (save[l]==x) return l;
    if (save[r]==x) return r;
    return n+1;
}
int sort(int l, int r){
    int i=l, j=r, key=b[(l+r)/2], temp;
    while (i<=j){
          while (b[i]<key) i++;
          while (b[j]>key) j--;
          if (i<=j) {
             temp=b[i]; b[i]=b[j]; b[j]=temp;
             i++; j--;
          }
    }
    if (l<j) sort(l,j);
    if (i<r) sort(i,r);
    return 0;
}
int roirac(){
    ForU( i,1,n) b[i]=a[i];
    sort(1,n);
    m=0;
    ForU( i,1,n) 
          if (b[i]!=b[i-1]) {
             m++;
             save[m]=b[i];
          }
    ForU( i,1,n) rr[i]=find(a[i]);
    return 0;
}
int main(){
    if (test) {
       freopen("input.txt","r",stdin);
       freopen("output.txt","w",stdout);
       }
    scanf("%d",&n);
    ForU( i,1,n) scanf("%d",&a[i]);
    roirac();
    
    int res=0,j=0;
    ForU( d,1,100) {
          ForU( i,1,m+1) last[i]=n+1;last[n+1]=n+1;
          ForD( i,n,1) {
                j=find(a[i]+d);
                next[i]=last[j];
                last[rr[i]]=i;
                f[i]=0;
          }
          ForU( i,1,n){
                f[i]+=1;
                if (res<f[i]) res=f[i];
                if (f[next[i]]<f[i]) f[next[i]] = f[i];
          }
    }
    cout<<res;
    return 0;
}
 
 

 
#include <fstream>
#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
#define ForU(i,a,b) for(int i=a;i<=b;i++)
#define ForD(i,a,b) for(int i=a;i>=b;i--)
int const test=0;
int const nmax=100009;
int a[nmax], b[nmax], save[nmax],
 f[nmax], rr[nmax], next[nmax], last[nmax];
int n,m;
int find(int x){
    if (x==save[1]) return 1;
    if (x==save[m]) return m;
    int l=1, r=m, t=0;
    while (r-l>1) {
          t=(l+r)/2;
          if (save[t]>x) r=t;
          else l=t;
    }
    if (save[l]==x) return l;
    if (save[r]==x) return r;
    return n+1;
}
int sort(int l, int r){
    int i=l, j=r, key=b[(l+r)/2], temp;
    while (i<=j){
          while (b[i]<key) i++;
          while (b[j]>key) j--;
          if (i<=j) {
             temp=b[i]; b[i]=b[j]; b[j]=temp;
             i++; j--;
          }
    }
    if (l<j) sort(l,j);
    if (i<r) sort(i,r);
    return 0;
}
int roirac(){
    ForU( i,1,n) b[i]=a[i];
    sort(1,n);
    m=0;
    ForU( i,1,n) 
          if (b[i]!=b[i-1]) {
             m++;
             save[m]=b[i];
          }
    ForU( i,1,n) rr[i]=find(a[i]);
    return 0;
}
int main(){
    if (test) {
       freopen("input.txt","r",stdin);
       freopen("output.txt","w",stdout);
       
       }
    scanf("%d",&n);
    ForU( i,1,n) scanf("%d",&a[i]);
    roirac();
    
    int res=0,j=0;
    ForU( d,1,100) {
          ForU( i,1,m+1) last[i]=n+1;last[n+1]=n+1;
          memset(f,0,sizeof(int)*(n+5));
          ForD( i,n,1) {
                j=find(a[i]+d);
                next[i]=last[j];
                last[rr[i]]=i;
                //f[i]=0;
          }
          ForU( i,1,n){
                f[i]+=1;
                if (res<f[i]) res=f[i];
                if (f[next[i]]<f[i]) f[next[i]] = f[i];
          }
          
    }
    cout<<res;
    return 0;
}