#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef long double ld;
#define F first
#define S second
#define pb push_back
#define endl '\n'
#define Mp make_pair
#define all(x) x.begin(), x.end()
#define debug(x) cerr << #x << " = " << x << endl;
#define fast_io ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io freopen("input19.txt" , "r" , stdin) ;
const int N = 523;
const ll mod=1e9+7;
ll power(ll a, ll b){
ll ans=1;
while(b){
if(b&1) ans=ans*a%mod;
b>>=1;
a=a*a%mod;
}
return ans;
}
ll inv[N];
ll dp[N][N];
ll L[N], R[N];
int n;
int main()
{
fast_io
for (int i=1; i<N; i++) inv[i]=power(i, mod-2);
cin>>n;
vector<ll> vec;
for (int i=1; i<=n; i++) {
cin>>L[i]>>R[i];
R[i]++;
vec.pb(L[i]);
vec.pb(R[i]);
}
sort(all(vec));
vec.resize(unique(all(vec))-vec.begin());
for (int j=0; j<N; j++) dp[0][j]=1;
for (int i=1; i<=n; i++){
int tl=lower_bound(all(vec), L[i])-vec.begin();
int tr=lower_bound(all(vec), R[i])-vec.begin();
for (int j=1; j<vec.size(); j++){
dp[i][j]=dp[i][j-1];
if(j<=tl || j>tr) continue;
int num=0;
ll za=1;
for (int pre=i-1; pre>=0; pre--){
if(L[pre+1]<=vec[j-1] && vec[j]<=R[pre+1]){
num++;
za=za*(vec[j]-vec[j-1]+num-1)%mod*inv[num]%mod;
}
dp[i][j]=(dp[i][j]+dp[pre][j-1]*za%mod)%mod;
}
}
}
ll ans=0;
int temp=vec.size();
for (int i=1; i<=n; i++) ans=(ans+dp[i][temp-1]);
cout<<ans<<endl;
}
