#include <bits/stdc++.h> using namespace std; #define int long long const int mod = 998244353, MAXN = 600; int qpow(int a, int b) { int ans = 1; while (b) { if (b & 1ll) ans = ans * a % mod; a = a * a % mod; b = b / 2ll; } return ans; } int n; int l[MAXN + 5], r[MAXN + 5]; int re[MAXN * 2 + 5], rcnt; int dp[MAXN + 5][MAXN * 2 + 5], C[MAXN * 2 + 5]; signed main() { scanf("%lld", &n); for (int i = 1; i <= n; i ++) { scanf("%lld%lld", &l[i], &r[i]); re[++ rcnt] = l[i]; re[++ rcnt] = ++ r[i]; } sort(re + 1, re + rcnt + 1); rcnt = unique(re + 1, re + rcnt + 1) - re - 1; for (int i = 1; i <= n; i ++) { l[i] = lower_bound(re + 1, re + rcnt + 1, l[i]) - re; r[i] = lower_bound(re + 1, re + rcnt + 1, r[i]) - re; } dp[0][rcnt] = 1; re[rcnt + 1] = 114514; for (int i = 1; i < rcnt; i ++) dp[0][i] = 1; for (int i = 1; i <= n; i ++) { for (int j = l[i]; j < r[i]; j ++) { int len = re[j + 1] - re[j]; C[1] = len; for (int k = 2; k <= i; k ++) C[k] = C[k - 1] * (len + k - 1) % mod * qpow(k, mod - 2) % mod; for (int k = i - 1; k >= 0; k --) { dp[i][j] = (dp[i][j] + dp[k][j + 1] * C[i - k] % mod) % mod; if (j < l[k] || j >= r[k]) break; } } for (int j = rcnt - 1; j >= 1; j --) dp[i][j] = (dp[i][j] + dp[i][j + 1]) % mod; } int ans = dp[n][1]; cout<<ans; return 0; }