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;
#define ll long long
const ll N = 2e5 + 10, MOD = 998244353;
ll dp[N], n, k, l[N], r[N];
int f(ll l, ll r) {
    if(l > r || r <= 0) return 0;
    l = max(l, 1ll);
    r = min(r, n);
    return (MOD + dp[r] - dp[l - 1]) % MOD;
}
int main() {
    cin >> n >> k;
    for(int i = 1; i <= k; ++i) {
        cin >> l[i] >> r[i];
    }
    dp[1] = 1;
    for(int i = 2; i <= n; ++i) {
        dp[i] = dp[i - 1];
        for(int j = 1; j <= k; ++j) {
            dp[i] = (dp[i] + f(i - r[j], i - l[j])) % MOD;
        }
    }
    cout << (MOD + dp[n] - dp[n - 1]) % MOD << endl;
}