Code

#include <atcoder/modint>
#include <bits/stdc++.h>

using namespace std;
using namespace atcoder;

using mint = modint998244353;

void solve(int n, vector<int> &L, vector<int> &R) {
    int k = L.size();

    vector<mint> difference_array_of_dp(n + 2, 0);

    // Difference array should always be modified in pairs. Just because
    // dp[1] = 1, doesn't mean you can set diff_array[1] = 1
    difference_array_of_dp[1] = 1;
    difference_array_of_dp[1 + 1] -= 1;
    mint running_sum = 0;
    for (int i = 1; i <= n; i++) {
        running_sum += difference_array_of_dp[i];
        mint current_dp = running_sum;
        for (int j = 0; j < k; j++) {
            if (i + L[j] > n) {
                continue;
            }
            int left = i + L[j];
            int right = min(i + R[j], n);
            difference_array_of_dp[left] += current_dp;
            difference_array_of_dp[right + 1] -= current_dp;
        }
    }

    cout << running_sum.val() << endl;
}

int main() {
    int n, k;
    cin >> n >> k;
    vector<int> L(k), R(k);
    for (int i = 0; i < k; i++) {
        cin >> L[i] >> R[i];
    }
    solve(n, L, R);
    return 0;
}

#include <atcoder/modint>
#include <bits/stdc++.h>

using namespace std;
using namespace atcoder;

using mint = modint998244353;

void solve(int n, vector<int> &L, vector<int> &R) {
    int k = L.size();

    vector<mint> dp(n + 1, 0);
    dp[1] = 1;
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < k; j++) {
            for (int d = L[j]; d <= R[j]; d++) {
                if (i + d <= n) {
                    dp[i + d] += dp[i];
                }
            }
        }
    }

    cout << dp[n].val() << endl;
}

int main() {
    int n, k;
    cin >> n >> k;
    vector<int> L(k), R(k);
    for (int i = 0; i < k; i++) {
        cin >> L[i] >> R[i];
    }
    solve(n, L, R);
    return 0;
}