#include<cstdio>
#include<math.h>
#include<algorithm>

using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
const int INF=1001001001;
int N,K;
bool W=false;
int A[100002];
pair<int,int> R[100002];//????????¨??????


int main(){
	while(1){
	scanf("%d %d",&N,&K);
	if(N==0&&K==0)break;
	rep(i,K){
		int a;
		scanf("%d",&a);
		if(a==0){i--;K--;W=true;continue;}
		A[i]=a;
	}
	sort(A,A+K);
	int rn=0;//?????°???????????????
	R[rn].first=A[0];
	rep(i,K){
		if(A[i]+1==A[i+1]){
		}else{
			R[rn].second=A[i];
			rn++;
			R[rn].first=A[i+1];
		}
	}
	R[rn].second=A[K-1];
	int ans=0;
	rep(i,rn){
		if(W==false){
			ans=max(ans,R[i].second-R[i].first+1);
		}else{
			ans=max(ans,R[i].second-R[i].first+2);
			if(i==rn-1)continue;
			if(R[i].second==R[i+1].first-2){
				ans=max(R[i+1].second-R[i].first+1,ans);
			}
		}
	}
	printf("%d\n",ans);
	}
}
### Prompt

In cpp, your task is to solve 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<cstdio>
#include<math.h>
#include<algorithm>

using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
const int INF=1001001001;
int N,K;
bool W=false;
int A[100002];
pair<int,int> R[100002];//????????¨??????


int main(){
	while(1){
	scanf("%d %d",&N,&K);
	if(N==0&&K==0)break;
	rep(i,K){
		int a;
		scanf("%d",&a);
		if(a==0){i--;K--;W=true;continue;}
		A[i]=a;
	}
	sort(A,A+K);
	int rn=0;//?????°???????????????
	R[rn].first=A[0];
	rep(i,K){
		if(A[i]+1==A[i+1]){
		}else{
			R[rn].second=A[i];
			rn++;
			R[rn].first=A[i+1];
		}
	}
	R[rn].second=A[K-1];
	int ans=0;
	rep(i,rn){
		if(W==false){
			ans=max(ans,R[i].second-R[i].first+1);
		}else{
			ans=max(ans,R[i].second-R[i].first+2);
			if(i==rn-1)continue;
			if(R[i].second==R[i+1].first-2){
				ans=max(R[i+1].second-R[i].first+1,ans);
			}
		}
	}
	printf("%d\n",ans);
	}
}
```