#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pair<int,int>> vpi;
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)
#define pb push_back
#define rsz resize
#define sz(x) int(x.size())
#define all(x) begin(x), end(x)
#define fi first
#define se second
// subtask 1 and 2
int const N=5e2+3;
ll a[N],b[N];
ll dp[N][2*N];
ll mod =1e9+7;
ll aps(ll n, ll d)
{
return (n*(2+(n-1)*d) / 2)%mod;
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0);
int n;
cin>>n;
set<ll> st;
F0R(i,n)
{
cin>>a[i]>>b[i];
--a[i];
st.insert(a[i]);
st.insert(b[i]);
}
st.insert(0);
vi v(all(st));
map<ll,ll>mp;
F0R(i,sz(st))
{
mp[v[i]]=i;
}
F0R(i,n)
{
a[i]=mp[a[i]];
b[i]=mp[b[i]];
}
F0R(j,sz(st)+1)
{
dp[0][j]=1;
}
dp[0][0]=0;
F0R(i,n)
{
F0R(j,sz(st))
{
dp[i+1][j+1]=dp[i][j+1]-dp[i][j];
dp[i+1][j+1]+=mod;
dp[i+1][j+1]%=mod;
}
FOR(j,a[i]+1,b[i]+1)
{
ll l = v[j]-v[j-1];
ll add = l * dp[i][j];
add%=mod;
dp[i+1][j+1]+=add;
dp[i+1][j+1]%=mod;
}
F0R(j,sz(st))
{
dp[i+1][j+1]+=dp[i+1][j];
dp[i+1][j+1]%=mod;
}
}
ll ans=dp[n][sz(st)]-1;
ans+=mod;
ans%=mod;
cout<<ans<<'\n';
return 0;
}
