#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main(){
	int n=0;
	int count=1;
	cin >> n;
	vector<int> size(n);
	for(int i=0;i<n;i++){
		cin>>size[i];
	}
	sort(size.begin(),size.end());
	for(int k=0;k<n;k++){
		if(size[k]+1==size[k+1]){
			count=2;
		}
		if(count == 2) break;
	}
	cout<<count<<endl;
}