#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 510;
const int MOD = 1e9+7;
ll a[N], b[N], l[2*N+1], dp[N][2*N+1], iv[N], n;
int main() {
cin>>n;
iv[1]=1;
for (int i=2; i<N; ++i) iv[i]=(iv[MOD%i]*(MOD-MOD/i))%MOD;
vector<int> v;
for (int i=1; i<=n; ++i) {
cin>>a[i]>>b[i];
v.push_back(a[i]), v.push_back(b[i]+1);
}
sort(v.begin(), v.end());
v.erase(unique(v.begin(), v.end()), v.end());
int sz=v.size();
for (int i=1; i<=n; ++i) {
a[i]=upper_bound(v.begin(), v.end(), a[i])-v.begin();
b[i]=upper_bound(v.begin(), v.end(), b[i])-v.begin();
}
for (int i=1; i<sz; ++i) l[i]=v[i]-v[i-1], dp[0][i]=1;
dp[0][0]=1;
for (int i=1; i<=n; ++i) {
for (int j=a[i]; j<=b[i]; ++j) {
dp[i][j]=(1ll*l[j]*dp[i-1][j-1])%MOD;
ll c=1, x=l[j]-1;
for (int k=i-1; k>0; --k) {
if (a[k] > j || b[k] < j) continue;
++c;
(x=(1ll*x*(l[j]+c-2)%MOD)*iv[c])%=MOD;
if (x == 0) break;
(dp[i][j]+=1ll*dp[k-1][j-1]*x)%=MOD;
}
} dp[i][0]=1;
for (int j=1; j<sz; ++j) dp[i][j]=(1ll*dp[i][j]+dp[i-1][j]+dp[i][j-1]-dp[i-1][j-1]+MOD)%MOD;
} cout<<(dp[n][sz-1]-1+MOD)%MOD<<"\n";
}
