#include<bits/stdc++.h>
#define pb push_back
#define x first
#define y second
#define all(a) (a).begin(), (a).end()
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
const int maxn = 1005;
const int MOD = 1e9 + 7;
int mult(ll a, ll b) {return (a * b) % MOD;}
int pot(int n, int k) {
int ret = 1, pot = n;
for(;k > 0;k >>= 1, pot = mult(pot, pot))
if(k & 1) ret = mult(ret, pot);
return ret;
}
int divide(int a, int b) {return mult(a, pot(b, MOD - 2));}
int add(int a, int b) {a += b;if(a >= MOD) a -= MOD;return a;}
int sub(int a, int b) {a -= b;if(a < 0) a += MOD;return a;}
int n, m;
int a[maxn], b[maxn];
int len[maxn], inv[maxn];
int dp[maxn][maxn];
vector<int> v;
int main() {
scanf("%d", &n);
for(int i = 1;i <= n;i++)
scanf("%d%d", a + i, b + i), b[i]++;
for(int i = 1;i <= n;i++)
inv[i] = divide(1, i);
for(int i = 1;i <= n;i++)
v.pb(a[i]), v.pb(b[i]);
sort(v.begin(), v.end());
v.resize(unique(all(v)) - v.begin());
for(int i = 1;i <= n;i++) {
a[i] = lower_bound(all(v), a[i]) - v.begin() + 1;
b[i] = lower_bound(all(v), b[i]) - v.begin() + 1;
}
m = (int)v.size() - 1;
for(int i = 1;i <= m;i++)
len[i] = v[i] - v[i - 1];
dp[0][0] = 1;
for(int i = 1;i <= m;i++){
dp[i][0] = 1;
for(int j = 1;j <= n;j++){
ll to_mul = len[i];
int cnt = 1;
dp[i][j] = dp[i - 1][j];
if(i < a[j] || i >= b[j]) continue;
for(int k = j - 1;k >= 0;k--) {
dp[i][j] = add(dp[i][j], mult(dp[i - 1][k], to_mul));
if(a[k] <= i && i < b[k]) {
to_mul = mult(mult(to_mul, add(cnt, len[i])), inv[cnt + 1]);
cnt++;
}
}
}
}
int ans = 0;
for(int i = 1;i <= n;i++)
ans = add(ans, dp[m][i]);
printf("%d\n", ans);
return 0;
}
