#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <vector>
#include <utility>
using namespace std;

int N,K;

int main() {
	while(true) {
		scanf("%d %d", &N, &K);
		if (N == 0) break;
		vector<bool> v(N+2);
		bool wc = false;
		for (int i = 0; i < K; ++i) {
			int c;
			scanf("%d", &c);
			if (c == 0) {
				wc = true;
			} else {
				v[c] = true;
			}
		}
		int ans = 0;
		vector<int> s,e;
		for (int i = 1; i <= N; ++i) {
			if (!v[i-1] && v[i]) s.push_back(i);
			if (v[i] && !v[i+1]) e.push_back(i);
		}
		for (size_t i = 0; i < s.size(); ++i) {
			ans = max(ans, e[i] - s[i] + 1);
		}
		if (wc) {
			if (K == 1) {
				ans = 1;
			} else {
				for (int i = 1; i <= N; ++i) {
					if (!v[i] && (v[i-1] || v[i+1])) {
						int p = i-1;
						int pc = 0;
						while (v[p]) {
							--p;
							++pc;
						}
						int n = i+1;
						int nc = 0;
						while (v[n]) {
							++n;
							++nc;
						}
						ans = max(ans, pc + nc + 1);
					}
				}
			}
		}
		cout << ans << endl;
	}
  return 0;
}
### Prompt

Construct a cpp code solution to the problem outlined:

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 <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <vector>
#include <utility>
using namespace std;

int N,K;

int main() {
	while(true) {
		scanf("%d %d", &N, &K);
		if (N == 0) break;
		vector<bool> v(N+2);
		bool wc = false;
		for (int i = 0; i < K; ++i) {
			int c;
			scanf("%d", &c);
			if (c == 0) {
				wc = true;
			} else {
				v[c] = true;
			}
		}
		int ans = 0;
		vector<int> s,e;
		for (int i = 1; i <= N; ++i) {
			if (!v[i-1] && v[i]) s.push_back(i);
			if (v[i] && !v[i+1]) e.push_back(i);
		}
		for (size_t i = 0; i < s.size(); ++i) {
			ans = max(ans, e[i] - s[i] + 1);
		}
		if (wc) {
			if (K == 1) {
				ans = 1;
			} else {
				for (int i = 1; i <= N; ++i) {
					if (!v[i] && (v[i-1] || v[i+1])) {
						int p = i-1;
						int pc = 0;
						while (v[p]) {
							--p;
							++pc;
						}
						int n = i+1;
						int nc = 0;
						while (v[n]) {
							++n;
							++nc;
						}
						ans = max(ans, pc + nc + 1);
					}
				}
			}
		}
		cout << ans << endl;
	}
  return 0;
}
```