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;
const int64_t MOD = 998244353;
const int64_t MAXN = 200100;
int64_t memo[MAXN * 2];

int main()
{
  int64_t N, K;
  cin >> N >> K;
  vector<int64_t> L(K), R(K);
  for (int i = 0; i < K; i++)
  {
    cin >> L.at(i) >> R.at(i);
  }
  memo[0] = 1;
  memo[1] = (MOD - 1) % MOD;
  for (int i = 0; i < N; i++)
  {
    if (i)
    {
      (memo[i] += memo[i - 1]) %= MOD;
    }
    int64_t cur = memo[i];
    for (int j = 0; j < K; j++)
    {
      int64_t l = L[j], r = R[j];
      (memo[i + l] += cur) %= MOD;
      (memo[i + r + 1] = memo[i + r + 1] - cur + MOD) %= MOD;
    }
  }
  cout << memo[N - 1] % MOD << endl;
}