#include <bits/stdc++.h>
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2")
//#pragma GCC optimize("unroll-loops")
#define rep(i,l,r) for (int i = l; i < r; i++)
#define repr(i,r,l) for (int i = r; i >= l; i--)
#define X first
#define Y second
#define all(x) (x).begin() , (x).end()
#define pb push_back
#define endl '\n'
#define debug(x) cerr << #x << " : " << x << endl;
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pll;
constexpr int N = 5e2+20,mod = 1e9+7 ,inf = 1e9+10,maxm = (1 << 10)+10;
inline int mkay(int a,int b){
if (a+b >= mod) return a+b-mod;
if (a+b < 0) return a+b+mod;
return a+b;
}
inline int poww(int a,int k){
if (k < 0) return 0;
int z = 1;
while (k){
if (k&1) z = 1ll*z*a%mod;
a = 1ll*a*a%mod;
k >>= 1;
}
return z;
}
int dp[2][2*N][N],sum[2][2*N];
int a[N],b[N],n,inv[N*2];
int main(){
vector<int> ve;
cin >> n;
ve.reserve(2*n);
rep(i,1,n+1){
cin >> a[i] >> b[i];
b[i]++;
ve.pb(a[i]);
ve.pb(b[i]);
}
sort(all(ve));
rep(i,1,n+1){
a[i] = lower_bound(all(ve),a[i])-ve.begin();
b[i] = lower_bound(all(ve),b[i])-ve.begin();
}
int nn = 2*n+1;
rep(i,0,n+2) inv[i] = poww(i,mod-2);
rep(i,1,n+1){
bool f = (i&1);
rep(j,0,nn){
sum[f][j] = 0;
rep(k,1,n+1){
if (k > i) break;
dp[f][j][k] = dp[1-f][j][k];
if (j < a[i] || j >= b[i]){
sum[f][j] = (sum[f][j]+dp[f][j][k])%mod;
continue;
}
if (k > 1){
dp[f][j][k] = (dp[f][j][k]+1ll*dp[1-f][j][k-1]*inv[k]%mod*(ve[j+1]-ve[j]-k+1)%mod)%mod;
}
else{
dp[f][j][k] = (dp[f][j][k]+ve[j+1]-ve[j])%mod;
rep(g,0,j){
dp[f][j][k] = (dp[f][j][k]+1ll*(ve[j+1]-ve[j])*sum[1-f][g]%mod)%mod;
}
}
sum[f][j] = (sum[f][j]+dp[f][j][k])%mod;
}
}
}
bool f = n%2;
int ans = 0;
rep(i,0,nn){
ans = (ans+sum[f][i])%mod;
}
cout << ans;
}
