#include<bits/stdc++.h>
#define FILE "read"
#define MAXN 50010
#define cmax(a,b) a=max(a,b)
#define cmin(a,b) a=min(a,b)
using namespace std;
typedef long long ll;
const int mod=1e7;
int n,ans,maxx,minn,a[MAXN],hash[mod+10];
inline int read(){
	int x=0,f=1;  char ch=getchar();
	while(ch>'9'||ch<'0')  {if(ch=='-')  f=-1;  ch=getchar();}
	while(ch>='0'&&ch<='9')  {x=x*10+ch-'0';  ch=getchar();}
	return x*f;
}
void Special_check(){
	int ret=1;  sort(a+1,a+n+1);
	for(int i=1;i<=n;++i){
		if(a[i]==a[i-1]) ++ret;
		else cmax(ans,ret),ret=1;
	}
}
int Hash(int x){
	int pos=x%mod; if(!pos) pos=mod;
	while(hash[pos]&&hash[pos]!=x) pos=pos%mod+1;
	return pos;
}
int find(int x){return hash[Hash(x)]==x;}
int main(){
	//freopen(FILE".in","r",stdin);
	//freopen(FILE".out","w",stdout);
	n=read();  minn=2e9;
	for(int i=1;i<=n;++i) a[i]=read();
	for(int i=1;i<=n;++i){
		cmax(maxx,a[i]);
		cmin(minn,a[i]);
	}
	Special_check();//特判公差为0的情况
	for(int i=1;i<=n;++i) hash[Hash(a[i])]=a[i];
	for(int i=1;i<=n;++i)for(int j=i+1;j<=n;++j){
		int D=a[j]-a[i],cur=2,ret=a[j];
		if((ll)a[i]+(ll)ans*D>maxx) continue;
		while(find(ret+D)) ++cur,ret+=D;
		cmax(ans,cur);
	}
	if(ans<200) puts("No Solution");
	else printf("%d\n",ans);
	//printf("%d\n",clock());
	return 0;
}