#include<bits/stdc++.h>
using namespace std;

#define ll long long
#define inf 0x7fffffff
#define SCD(t) scanf("%d",&t)
#define SCLD(t) scanf("%ld",&t)
#define SCLLD(t) scanf("%lld",&t)
#define SCC(t) scanf("%c",&t)
#define SCS(t) scanf("%s",t)
#define SCF(t) scanf("%f",&t)
#define SCLF(t) scanf("%lf",&t)
#define pr pair<int,int>
#define mp(a,b) make_pair(a,b)
#define pb push_back
#define fr first
#define sc second
#define mset(arr,val) memset(arr,val,sizeof(arr));

const int MAX = 1000005;
const int MOD = 1e9+7;

int freq[MAX];

int main(){
	// freopen("input.txt","r",stdin);
	int t;
	SCD(t);
	while(t--){
		int x;
		cin>>x;
		freq[x]++;

	}
	int ans = 2;
	for (int i = 0; i <= 100; ++i)
	{
		if(freq[i] + freq[i+1] > ans)
			ans = freq[i] + freq[i+1];
	}

	cout<<ans;
}