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<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<string>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int MAXN = 2e5 + 5;
const int MAXD = 10 + 5;
const int mod = 998244353;

int l[MAXN], r[MAXN];

ll f[MAXN], sum[MAXN];

int main(void)
{
	int n,d;
	scanf("%d%d",&n,&d);
	for(int i=1; i<=d; ++i)
		scanf("%d%d",&l[i],&r[i]);
	
	f[1] = sum[1] = 1;
	
	for(int i=2; i<=n; ++i)
	{
		for(int j=1; j<=d; ++j)
		{
			if(i - l[j] < 1) continue;
			
			f[i] = (f[i] + sum[i-l[j]] - sum[max(i-r[j],1)-1] + mod) %mod;
		}
		sum[i] = (sum[i-1] + f[i]) %mod;
	}
	printf("%lld",f[n]);
	return 0;
}