#include <bits/stdc++.h>
#pragma GCC optimize("O3", "Ofast")
#define int long long
#define ll long long
#define se second
#define fi first
#define pb push_back
#define lf (id<<1)
#define rg ((id<<1)|1)
#define md ((l+r)>>1)
using namespace std;
typedef pair<int,int> pii;
typedef pair<pii,pii> ipii;
const int MAXN = 1010;
const int MAXA = 2e5+10;
const int SQRT = 450;
const ll INF = 2e12;
const int MOD = 998244353;
const int LOG = 30;
int sum(int a, int b){
int te = a+MOD+b;
for(; te >= MOD; ) te -= MOD;
return te;
}
void chsum(int &a, int b){ a = sum(a,b); }
int mul(int a, int b){ return a*b%MOD; }
void chmul(int &a, int b){ a = mul(a,b); }
void chmn(auto &a, auto b){ a = min(a, b); }
void chmx(auto &a, auto b){ a = max(a, b); }
int expo(int a, int b){
if(b==0) return 1;
int te = expo(a, b/2); te = mul(te,te); // temporary -> te
return (b%2 ? mul(te, a) : te);
}
int n, k, l[MAXN], r[MAXN], val[MAXN][MAXN], dp[MAXN][MAXN], pr[MAXN][MAXN];
int inv[MAXN], way[MAXN][MAXN];
vector<pii> seg;
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>n;
vector<int> cc; cc.pb(-1);
for(int i=1; i<=n; i++){
cin>>l[i]>>r[i];
cc.pb(l[i]); cc.pb(r[i]+1);
}
sort(cc.begin(), cc.end());
cc.resize(unique(cc.begin(), cc.end())-cc.begin());
seg.pb({-1, -1});
for(int i=1; i+1<cc.size(); i++) seg.pb({cc[i], cc[i+1]-1});
k = seg.size()-1;
for(int i=1; i<=n; i++){
for(int j=1; j<=k; j++){
if(l[i]<=seg[j].fi && seg[j].se<=r[i]) val[i][j] = 1;
}
}
inv[0] = 1; int run = 1;
for(int i=1; i<=n; i++){
chmul(run, i);
inv[i] = expo(run, MOD-2);
}
for(int j=1; j<=k; j++){
for(int i=1; i<=n; i++){
int te = 1, siz = seg[j].se-seg[j].fi+1;
if(siz < i){ way[j][i] = 0; continue; }
for(int p=siz; p>=siz-i+1; p--) chmul(te, p);
chmul(te, inv[i]);
way[j][i] = te;
// cout << j << ' '<< i << ' '<<way[j][i] <<" ywa\n";
}
}
// for(auto [x,y] : seg) cout << x << ' ' << y << " y\n";
for(int i=1; i<=n; i++){
for(int j=1; j<=k; j++){
// dp[i][j]
int te = 0;
bool can = 1;
for(int ba=i; ba>=1; ba--){
if(val[ba][j] == 0) can = 0;
int nw = way[j][i-ba+1]; // C(seg[j].se-seg[j].fi+1, i-ba+1)
if(can) chsum(te, nw);
}
dp[i][j] = sum(dp[i][j-1], mul(te, sum(1, pr[i-1][j-1]) ) );
pr[i][j] = sum(pr[i-1][j], dp[i][j]);
// cout << dp[i][j] << ' '<< i << ' '<< j << " ij\n";
}
}
cout << pr[n][k] << '\n';
}
