#include<bits/stdc++.h>

using namespace std;

#define gc getchar_unlocked

#define rep(i,j,k) for(i=j; i<k; i++)
#define rrep(i,j,k) for(i=j; i>=k; i--)

typedef long long ll;
typedef vector<int> vi;
typedef vector<string> vs;


int main(){
    int n;
    cin >> n;
    int a[n],b[101];
    memset(b,0,sizeof(b));
    
    int i;
    rep(i,0,n)
        {
        cin>>a[i];
        b[a[i]]++;
    }
    int max = b[1]+b[2];
    rep(i,2,100)
        {
        if(b[i] + b[i+1] > max)
            max = b[i] + b[i+1];
    }
    cout<<max;
    
    
    return 0;
}