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>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
 
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using ll = long long;
using P = pair<int, int>;

#define INF 1001001001
#define MAX 1e18

const int mod = 998244353;

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