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>
using namespace std;
#define ll long long
#define all(V) V.begin(),V.end()
const ll MOD = 998244353;

ll R[11], L[11], S[800010];

int main() {
	int N, K;
	cin >> N >> K;
	
	for (int i = 0;i < K;i++) {
		cin >> L[i] >> R[i];
	}
	for (int i = 0;i < 800010;i++)S[i] = 0;
	S[1] = 1, S[2] = -1;
	for (int i = 1;i <= N;i++) {
		S[i] += S[i - 1];
		for (int k = 0;k < K;k++) {
			S[i + L[k]] += S[i];
			S[i + R[k] + 1] += -S[i];

			S[i + L[k]] %= MOD;
			S[i + R[k] + 1] %= MOD;
		}
	}
	S[N] %= MOD;
	S[N] += MOD;
	cout << S[N] % MOD << endl;
}