#include<bits/stdc++.h>
using namespace std;
const int N=510, mod=1e9+7;
int fact[N*2], invfact[N*2], inv[N*2];
int binpow(int x, int y){
int t=1;
while (y){
if (y&1) t=1ll*t*x%mod;
x=1ll*x*x%mod;
y>>=1;
}
return t;
}
void precalc(){
fact[0]=1;
for (int i=1; i<N*2; ++i) fact[i]=1ll*fact[i-1]*i%mod;
invfact[N*2-1]=binpow(fact[N*2-1], mod-2);
for (int i=N*2-2; i>=0; --i) invfact[i]=1ll*invfact[i+1]*(i+1)%mod;
for (int i=1; i<N*2; ++i) inv[i]=1ll*invfact[i]*fact[i-1]%mod;
}
int C(int n, int k){
if (n<0 || k<0 || n<k) return 0;
return 1ll*fact[n]*invfact[k]%mod*invfact[n-k]%mod;
}
int f[N*2][N], g[N*2][N], sf[N*2], sg[N*2], n, a[N], b[N];
vector<int> vals;
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
precalc();
vals.push_back(-1);
cin >> n;
for (int i=1; i<=n; ++i) cin >> a[i] >> b[i], vals.push_back(a[i]), vals.push_back(++b[i]);
sort(vals.begin(), vals.end());
vals.resize(unique(vals.begin(), vals.end())-vals.begin());
for (int i=1; i<=n; ++i){
a[i]=lower_bound(vals.begin(), vals.end(), a[i])-vals.begin();
b[i]=lower_bound(vals.begin(), vals.end(), b[i])-vals.begin();
}
f[0][0]=1;
for (int i=0; i<(int)vals.size(); ++i) sf[i]=1;
for (int i=1; i<=n; ++i){
for (int j=a[i]; j<b[i]; ++j){
int len=vals[j+1]-vals[j];
for (int k=1; k<=i && k<=len; ++k){
g[j][k]=(g[j][k]+1ll*(k==1?sf[j-1]:f[j][k-1])*(len-k+1)%mod*inv[k])%mod;
}
}
for (int j=0; j<(int)vals.size(); ++j) for (int k=0; k<=i; ++k){
g[j][k]=(g[j][k]+f[j][k])%mod;
sg[j]=(sg[j]+g[j][k])%mod;
}
for (int j=1; j<(int)vals.size(); ++j) sg[j]=(sg[j]+sg[j-1])%mod;
memcpy(f, g, sizeof f);
memcpy(sf, sg, sizeof sf);
memset(g, 0, sizeof g);
memset(sg, 0, sizeof sg);
}
cout << (sf[(int)vals.size()-1]+mod-1)%mod << '\n';
return 0;
}
