#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
using namespace std;
int cl(int a, int b) {
	return (a - (a%b)) / b;//b=0だと積む
}
int up(int a, int b) {
	return cl(a + b - 1, b);//b=0だと積む
}
int main() {
	int a, b, n, k;
	cin >> n >> k;
	while(n+k!=0){
	int ch = 0; int ans = 0; int n0 = 0;
	vector<int> c(n,0);
	for (int i = 0; i < k; i++) {
		int x;
		cin >> x;
		if (x != 0) {
			c[x - 1] = 1;
		}
		else {
			n0 = 1;
		}
	}
	vector<int> p(n+1,0);
	vector<int> q(n + 1, 0);
	int ba = 0;
	for (int i = 0; i < n; i++) {
		if (c[i] == 1) {
			p[ch]++;
			if (i >= 2) {
				if (c[i - 1] == 0 and c[i - 2] == 1) {
					q[ch] = 1;
				}
			}
		}
		if (c[i] == 0 and ba==1) {
			ch++;
		}
		ba = c[i];
	}
	for (int i = 1; i <= n; i++) {
		ans = max(ans, q[i] * n0*(p[i]+p[i-1]+1));
	}
	sort(p.begin(), p.end());
	ans = max(ans, p[n]);
	cout << ans<<endl;
	cin >> n >>k;
	}
}


### Prompt

Please formulate a cpp solution to the following problem:

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<iostream>
#include<vector>
#include<algorithm>
#include<string>
using namespace std;
int cl(int a, int b) {
	return (a - (a%b)) / b;//b=0だと積む
}
int up(int a, int b) {
	return cl(a + b - 1, b);//b=0だと積む
}
int main() {
	int a, b, n, k;
	cin >> n >> k;
	while(n+k!=0){
	int ch = 0; int ans = 0; int n0 = 0;
	vector<int> c(n,0);
	for (int i = 0; i < k; i++) {
		int x;
		cin >> x;
		if (x != 0) {
			c[x - 1] = 1;
		}
		else {
			n0 = 1;
		}
	}
	vector<int> p(n+1,0);
	vector<int> q(n + 1, 0);
	int ba = 0;
	for (int i = 0; i < n; i++) {
		if (c[i] == 1) {
			p[ch]++;
			if (i >= 2) {
				if (c[i - 1] == 0 and c[i - 2] == 1) {
					q[ch] = 1;
				}
			}
		}
		if (c[i] == 0 and ba==1) {
			ch++;
		}
		ba = c[i];
	}
	for (int i = 1; i <= n; i++) {
		ans = max(ans, q[i] * n0*(p[i]+p[i-1]+1));
	}
	sort(p.begin(), p.end());
	ans = max(ans, p[n]);
	cout << ans<<endl;
	cin >> n >>k;
	}
}


```