#include <bits/stdc++.h>
using namespace std;
#define int ll
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define X first
#define Y second
#define SZ(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define mins(a,b) a = min(a,b)
#define maxs(a,b) a = max(a,b)
#define pb push_back
#define Mp make_pair
#define kill(x) {cout << x << '\n'; exit(0);}
#define killt(x) {cout << x << '\n'; return;}
#define md(x) (((x%MOD)+MOD)%MOD)
#define lc id<<1
#define rc lc|1
#define mid ((l+r)/2)
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
const ll INF = 1e9 + 23;
const ll MOD = 1e9 + 7;
const int MXN = 1023;
const int LOG = 23;
ll power(ll a, ll b) {
ll res=1;
while(b) {
if(b&1) res = md(res*a);
a = md(a*a);
b >>= 1;
}
return res;
}
ll I[MXN];
void prep() {
for(int i=1; i<MXN; i++) I[i] = power(i, MOD-2);
}
int n, l[MXN], r[MXN];
vector<ll> cmp;
ll dp[MXN][MXN];
void Main() {
prep();
cin >> n;
for(int i=1; i<=n; i++) {
cin >> l[i] >> r[i];
cmp.pb(l[i]);
cmp.pb(++r[i]);
}
sort(all(cmp));
cmp.resize(unique(all(cmp))-cmp.begin());
int m = SZ(cmp);
for(int i=0; i<MXN; i++) dp[0][i] = 1;
for(int i=1; i<=n; i++) {
for(int j=1; j<m; j++) {
dp[i][j] = dp[i][j-1];
if(l[i]>cmp[j-1] || r[i]<cmp[j]) continue;
int t=0;
ll C = 1;
for(int k=i-1; k>=0; k--) {
if(l[k+1]<=cmp[j-1] && cmp[j]<=r[k+1]) {
t++;
C = md(C*md((cmp[j]-cmp[j-1]+t-1)*I[t]));
}
dp[i][j] = md(dp[i][j] + dp[k][j-1]*C);
}
}
}
ll ans=0;
for(int i=1; i<=n; i++)
ans = md(ans+dp[i][m-1]);
cout << ans << '\n';
}
int32_t main() {
cin.tie(0); cout.tie(0); ios_base::sync_with_stdio(0);
int T = 1;
// cin >> T;
while(T--) Main();
return 0;
}
