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;
typedef long long ll;
typedef pair<int,int> P;
#define rep(i,m,n) for(int i=m;i<n;i++)
const ll mod=998244353;

int main(){
  int n,k;
  cin>>n>>k;
  int l[k],r[k];
  rep(i,0,k) cin>>l[i]>>r[i];
  ll a[n];
  rep(i,0,n) a[i]=0;
  a[0]=1;
  ll sum[n+1];
  sum[0]=0;
  sum[1]=1;
  rep(i,1,n){
    rep(j,0,k){
      if(i-l[j]+1>=0) a[i]+=sum[i-l[j]+1];
      if(i-r[j]>=0) a[i]-=sum[i-r[j]];
      if(a[i]<0) a[i]+=mod;
      if(a[i]>mod) a[i]-=mod;
    }
    sum[i+1]=sum[i]+a[i];
    if(sum[i+1]>mod) sum[i+1]-=mod;
  }
  cout<<a[n-1]<<endl;
}