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 rep(i,a,n) for (int i=a; i<n; i++)
#define ll long long
#define MOD 998244353
using namespace std;;
 
int main() {
  int N, K; cin >> N >> K;
  vector<int> L(K),R(K); rep(i,0,K) cin >> L[i] >> R[i];
  vector<ll> dp(N + 1, 0); dp[0] = 1; dp[1] = -1;
  rep(i,0,N) { 
    dp[i] = ((dp[i] % MOD) + MOD) % MOD;
    dp[i + 1] = (dp[i + 1] + dp[i]) % MOD;
    rep(j,0,K) {
      if (i + L[j] < N) dp[i + L[j]] += dp[i];
      if (i + R[j] + 1 < N) dp[i + R[j] + 1] -= dp[i];
    }
  }
  cout << dp[N - 1] << endl;
}