#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;
using ll = int;
const ll mod = 1e9+7;
#define fi first
#define se second
#define rep(i,n) for(ll i=0;i<n;i++)
#define all(x) x.begin(),x.end()
#define faster ios::sync_with_stdio(false);cin.tie(nullptr)
ll modpow(long long A,ll N){
long long res=1;
while(N){
if(N&1) res=res*A%mod;
A=A*A%mod;
N>>=1;
}
return res;
}
ll modinv(ll A){return modpow(A,mod-2);}
int main() {
ll N;
cin >> N;
vector<ll> inv(N+1);
rep(i,N+1) inv[i]=modinv(i);
vector<ll> A(N),B(N);
rep(i,N){
cin >> A[i] >> B[i];
B[i]++;
}
vector<ll> C;
C.push_back(0),C.push_back(1);
rep(i,N) C.push_back(A[i]),C.push_back(B[i]);
sort(all(C));
C.erase(unique(all(C)),C.end());
rep(i,N) A[i]=lower_bound(all(C),A[i])-C.begin();
rep(i,N) B[i]=lower_bound(all(C),B[i])-C.begin();
ll M=C.size();
vector<ll> D(M-1);
rep(i,M-1) D[i]=C[i+1]-C[i];
vector<vector<vector<ll>>> dp(2,vector<vector<ll>>(M,vector<ll>(N,0)));
dp[0][0][0]=1;
vector<vector<vector<ll>>> cum(2,vector<vector<ll>>(M,vector<ll>(N,0)));
rep(j,M) cum[0][j][0]=1;
rep(i,N){
rep(j,M) rep(k,min(N,i+10)) dp[(i+1)%2][j][k]=0;
for(ll j=A[i];j<B[i];j++){
long long sumres=0;
rep(k,N) sumres+=cum[i%2][j-1][k];
sumres%=mod;
sumres*=D[j];
sumres%=mod;
dp[(i+1)%2][j][0]=sumres;
rep(k,min(N-1,i+10)){
if(D[j]<k+2) break;
long long res=(long long)(cum[i%2][j][k]+mod-cum[i%2][j-1][k])*(long long)(((long long)(D[j]-k-1)*(long long)(inv[k+2]))%mod);
res%=mod;
dp[(i+1)%2][j][k+1]=res;
}
}
rep(k,min(N,i+10)){
long long sum=0;
rep(j,M){
sum+=dp[(i+1)%2][j][k];
cum[(i+1)%2][j][k]=(cum[i%2][j][k]+sum)%mod;
}
}
}
ll ans=mod-1;
rep(k,N){
ans+=cum[N%2][M-1][k];
if(ans>=mod) ans-=mod;
}
cout << ans << endl;
return 0;
}
