Problem: There are N cells arranged in a row, numbered 1, 2, \ldots, N from left to right.

Tak lives in these cells and is currently on Cell 1. He is trying to reach Cell N by using the procedure described below.

You are given an integer K that is less than or equal to 10, and K non-intersecting segments [L_1, R_1], [L_2, R_2], \ldots, [L_K, R_K]. Let S be the union of these K segments. Here, the segment [l, r] denotes the set consisting of all integers i that satisfy l \leq i \leq r.

* When you are on Cell i, pick an integer d from S and move to Cell i + d. You cannot move out of the cells.



To help Tak, find the number of ways to go to Cell N, modulo 998244353.

Constraints

* 2 \leq N \leq 2 \times 10^5
* 1 \leq K \leq \min(N, 10)
* 1 \leq L_i \leq R_i \leq N
* [L_i, R_i] and [L_j, R_j] do not intersect (i \neq j)
* All values in input are integers.

Input

Input is given from Standard Input in the following format:


N K
L_1 R_1
L_2 R_2
:
L_K R_K


Output

Print the number of ways for Tak to go from Cell 1 to Cell N, modulo 998244353.

Examples

Input

5 2
1 1
3 4


Output

4


Input

5 2
3 3
5 5


Output

0


Input

5 1
1 2


Output

5


Input

60 3
5 8
1 3
10 15


Output

221823067

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
#define int long long
using namespace std;
const int mod=998244353;

int n,k;
int l[1005],r[1005],dp[1000005],pre[2000005];

inline int query(int ll,int rr)
{
	return ((pre[rr]-pre[ll-1])%mod+mod)%mod;
}

signed main()
{
	cin>>n>>k;
	for (int i=1;i<=k;i++)  cin>>l[i]>>r[i];
	
	dp[1]=1;
	for (int i=1;i<=n;i++)
	{
		for (int j=1;j<=k;j++)
		{
			if (l[j]>=i)  continue;
			int nowr=min(r[j],i-1ll);
			dp[i]=(dp[i]+max(query(i-nowr,i-l[j]),0ll))%mod;
		}
		pre[i]=(pre[i-1]+dp[i])%mod;
	}
	cout<<dp[n]%mod<<endl;
	
	return 0;
}