#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> mp;
#define inf 1e9


int main(){
	while(1){
		int n,k;
		cin>>n>>k;
		if(n==0) break;
		vector<int> dp(n+1,0);
		for(int i=0;i<k;i++){
			int tmp;
			cin>>tmp;
			dp[tmp] = 1;
		}
		int res = 0;
		for(int i=2;i<=n;i++){
			if(dp[i] == 1){
				dp[i] += dp[i-1];
				res = max(dp[i],res);
			}
		}
		/*for(int i=0;i<=n;i++){
			cout<<i<<' '<<dp[i]<<endl;
		}*/
		for(int i=n-1;i>=1;i--){
			if(dp[i] != 0 && dp[i+1] != 0){
				dp[i] = dp[i+1];
			}
		}
		if(dp[0] == 1){
			for(int i=2;i<n;i++){
				if(dp[i] == 0){
					res = max(res,dp[i-1]+dp[i+1] + 1);
					//cout<<i<<' '<<dp[i-1]<<' '<<dp[i+1]<<endl;
				}
			}
		}
		/*for(int i=0;i<=n;i++){
			cout<<i<<' '<<dp[i]<<endl;
		}*/
		cout<<res<<endl;
	}

	return 0;
}


### Prompt

Please provide a CPP coded solution to the problem described below:

problem

There are n cards with one integer from 1 to n and one blank card. Of these n + 1 cards, k cards are given, but 1 ≤ k ≤ n. You can write one integer from 1 to n on a blank card. I want to make a continuous sequence of integers as long as possible with just a given card.

Write a program that outputs the maximum length of a contiguous sequence of integers that can be made from a given card when the given card is entered.



input

The input consists of multiple datasets. Each dataset is given in the following format. The input ends on a line containing two zeros.

On the first line, two integers n (1 ≤ n ≤ 100000) and k (1 ≤ k ≤ n) are written in this order, separated by one blank. The following k line contains one integer. Written one by one, representing the integers written on the given k cards. Blank cards are represented by 0.

Of the scoring data, 40% of the points are 1 ≤ n ≤ 1000, 1 ≤ k ≤ 500, 20% of the points are 1 ≤ n ≤ 60000, 1 ≤ k ≤ 50000. Satisfy 1 ≤ n ≤ 100000, 1 ≤ k ≤ 100000.

The number of datasets does not exceed 5.

output

Outputs an integer on one line for each dataset.

Examples

Input

7 5
6
2
4
7
1
7 5
6
2
0
4
7
0 0


Output

2
4


Input

None


Output

None

### Response

```cpp
#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> mp;
#define inf 1e9


int main(){
	while(1){
		int n,k;
		cin>>n>>k;
		if(n==0) break;
		vector<int> dp(n+1,0);
		for(int i=0;i<k;i++){
			int tmp;
			cin>>tmp;
			dp[tmp] = 1;
		}
		int res = 0;
		for(int i=2;i<=n;i++){
			if(dp[i] == 1){
				dp[i] += dp[i-1];
				res = max(dp[i],res);
			}
		}
		/*for(int i=0;i<=n;i++){
			cout<<i<<' '<<dp[i]<<endl;
		}*/
		for(int i=n-1;i>=1;i--){
			if(dp[i] != 0 && dp[i+1] != 0){
				dp[i] = dp[i+1];
			}
		}
		if(dp[0] == 1){
			for(int i=2;i<n;i++){
				if(dp[i] == 0){
					res = max(res,dp[i-1]+dp[i+1] + 1);
					//cout<<i<<' '<<dp[i-1]<<' '<<dp[i+1]<<endl;
				}
			}
		}
		/*for(int i=0;i<=n;i++){
			cout<<i<<' '<<dp[i]<<endl;
		}*/
		cout<<res<<endl;
	}

	return 0;
}


```