#include <bits/stdc++.h>
using namespace std;
int main() {
	int n;cin>>n;
	vector<int> v;
	int mx=INT_MIN;
	for(int i=0;i<n;i++){
		int vl;cin>>vl;
		mx=max(mx,vl);
		v.push_back(vl);
	}
	vector<bool> vis(mx+1,false);
	for(int i=0;i<n;i++){
		vis[v[i]]=true;
	}
	int res=0,c=0;
	for(int i=0;i<mx;){
		if(vis[i]==false){
			i++;
		}
		else{
		while(vis[i]==true){
			i++;
			c++;
		}
		}
		res=max(res,c);
		c=0;
	}
	cout<<res<<" ";
	return 0;
}

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

MTIKMSA5IDMgMCAxOCA1IDIgNCAxMCA3IDEyIDY=

12
1 9 3 0 18 5 2 4 10 7 12 6