#include<bits/stdc++.h>
using namespace std;
int longlong(vector<int>&a){
	if(a.empty()){
		return 0;
	}
	sort(a.begin(),a.end());
	int longn=1;
	int nown=1;
	for(size_t i=1;i<a.size();i++){
		if(a[i]==a[i-1]+1){
			nown++;
		}else{
			longn=max(longn,nown);
			nown=0;
		}
	}
	longn=max(longn,nown);
	return longn;
}
int main() {
    vector <int>a;
    int n;
    cin>>n;
    int f[11514];
    for(int i=0;i<n;i++){
		cin>>f[i];
		a.push_back(f[i]);
	}
    cout<<longlong(a)+1;
    return 0;
}