#include <bits/stdc++.h>
using namespace std;
#define long long long
const long MOD = 1e9+7, LINF = 1e18 + 1e16;
const int INF = 1e9+1;
const double EPS = 1e-10;
const int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
const int N = 1010;
class APIO16_boat {
void add(long &a, long b) {
a += b;
if(a >= MOD) a -= MOD;
}
long mul(long a, long b) { return a*b % MOD; }
long modPow(long b, long e) {
if(e == 0) return 1;
if(e == 1) return b;
return mul(modPow(mul(b, b), e >> 1), modPow(b, e & 1));
}
int n, a[N], b[N];
pair<int,int> segs[N];
vector<int> vals;
unordered_map<int, int> rev;
long ans, inv[N], C[N][N], f[N][N], dp[N][N];
public:
void solve(istream &cin, ostream &cout) {
cin >> n;
vals.push_back(0);
for(int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
vals.push_back(a[i]);
vals.push_back(b[i]+1);
}
sort(vals.begin(), vals.end());
vals.resize(unique(vals.begin(), vals.end()) - vals.begin());
for(int i = 0; i < vals.size(); i++) rev[vals[i]] = i;
for(int i = 1; i <= n; i++) segs[i] = {rev[a[i]], rev[b[i]+1]};
inv[0] = 1;
for(int i = 1; i <= n; i++) inv[i] = modPow(i, MOD-2);
C[0][0] = 1;
for(int i = 1; i <= n; i++) {
C[i][0] = C[i][i] = 1;
for(int j = 1; j < i; j++) {
add(C[i][j], C[i-1][j-1]);
add(C[i][j], C[i-1][j]);
}
}
for(int j = 1; j < vals.size()-1; j++) {
f[j][0] = 1;
for(int cnt = 1; cnt <= min(vals[j+1] - vals[j], n); cnt++) {
f[j][cnt] = mul(f[j][cnt - 1], vals[j+1] - vals[j] - (cnt - 1));
f[j][cnt] = mul(f[j][cnt], inv[cnt]);
}
for(int cnt = n; cnt >= 1; cnt--) {
for(int x = 1; x <= min(cnt-1, n); x++) {
add(f[j][cnt], mul(f[j][x], C[cnt-1][x-1]));
}
}
}
for(int j = 0; j < vals.size(); j++) dp[0][j] = 1;
for(int i = 1; i <= n; i++) {
for(int j = segs[i].first; j < segs[i].second; j++) {
int cnt = 0;
for(int k = i-1; k >= 0; k--) {
cnt += segs[k+1].first <= j && j < segs[k+1].second;
add(dp[i][j], mul(dp[k][j-1], f[j][cnt]));
}
}
for(int j = 1; j < vals.size(); j++) add(dp[i][j], dp[i][j-1]);
add(ans, dp[i][vals.size() - 1]);
}
cout << ans << endl;
}
};
class Solver {
public:
void solve(std::istream& in, std::ostream& out) {
APIO16_boat *obj = new APIO16_boat();
obj->solve(in, out);
delete obj;
}
};
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
Solver solver;
std::istream& in(std::cin);
std::ostream& out(std::cout);
solver.solve(in, out);
return 0;
}
