#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define sz(a) (int)(a.size())
#define all(a) a.begin(),a.end()
#define lb lower_bound
#define ub upper_bound
#define owo ios_base::sync_with_stdio(0);cin.tie(0);
#define MOD (ll)(1e9+7)
#define INF (ll)(1e18)
#define debug(...) fprintf(stderr, __VA_ARGS__),fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false);\
debug("%s time : %.4fs\n", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))
typedef long long int ll;
typedef long double ld;
typedef pair<ll,ll> PII;
typedef pair<int,int> pii;
typedef vector<vector<int>> vii;
typedef vector<vector<ll>> VII;
ll gcd(ll a,ll b){if(!b)return a;else return gcd(b,a%b);}
ll A[550];
ll B[550];
ll len[1050];
ll inv[551];
ll dp[550][1050];
int main()
{
inv[1] = 1;
for (int i=2;i<550;i++) inv[i] = (ll)inv[MOD % i] * (MOD - MOD/i) % MOD;
int n;
cin>>n;
vector<ll>coords;
for(int i=1;i<=n;i++){
cin>>A[i];coords.pb(A[i]);
cin>>B[i];coords.pb(B[i]+1);
}
sort(all(coords));
coords.resize(unique(all(coords))-coords.begin());
for(int i=1;i<=n;i++){
A[i] = ub(all(coords),A[i])-coords.begin();
B[i] = ub(all(coords),B[i])-coords.begin();
}
for(int i=1;i<sz(coords);i++)len[i] = coords[i] - coords[i-1];
for(int i=0;i<sz(coords);i++)dp[0][i] = 1;
for(int i=1;i<=n;i++){
for(int j=A[i];j<=B[i];j++){
dp[i][j] = (dp[i-1][j-1]*len[j])%MOD;
ll choose = len[j]-1;
ll cnt = 1;
for(int k=i-1;k>0;k--){
if(A[k] <= j && j <= B[k]){
cnt++;
choose = (choose*(len[j]+cnt-2))%MOD;
choose = (choose*inv[cnt])%MOD;
if(!choose)break;
dp[i][j]=(dp[i][j]+dp[k-1][j-1]*choose)%MOD;
}
}
}
dp[i][0] = 1;
for(int j=1;j<sz(coords);j++){
dp[i][j]=(dp[i][j]+dp[i-1][j]+dp[i][j-1]-dp[i-1][j-1]+MOD)%MOD;
}
}
cout<<(dp[n][sz(coords)-1]+MOD-1)%MOD<<'\n';
}
