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;

int main(){
  const int64_t mod=998244353;
  int N,K;
  cin >> N >> K;
  vector<pair<int,int> > vp(K);
  for(int i=0;i<K;i++){
    cin >> vp.at(i).first >> vp.at(i).second;
  }
  vector<int64_t> dp(N+1,0),sum(N+1,0);
  dp.at(1)=1;
  sum.at(1)=sum.at(0)+dp.at(1);
  for(int i=2;i<=N;i++){
    for(int j=0;j<K;j++){
      if(i>vp.at(j).first){
        dp.at(i)+=(sum.at(i-vp.at(j).first)-sum.at(max(0,i-vp.at(j).second-1)))%mod;
        dp.at(i)%=mod;
      }
    }
    sum.at(i)+=(sum.at(i-1)+dp.at(i))%mod;
    sum.at(i)%=mod;
  }
  if(dp.at(N)<0){
    dp.at(N)+=mod;
  }
  cout << dp.at(N) << endl;
  return 0;
}