#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef pair<int,int> pi;
typedef vector<pi> pii;
typedef tuple<ll,ll,ll> ti;
typedef vector<ll> li;
typedef vector<li> lii;
#define REP(i,a,b) for(int i=a;i<b;i++)
#define F first
#define S second
#define PB push_back
#define LSOne(s) ((s)&(-s))
ll INF=1000000000000000010;
int inf=1e9+10;
int M=1e9+7;
int main() {
// ios::sync_with_stdio(0);
// cin.tie(0);
int n;cin>>n;
vector<pi> a(n);
REP(i,0,n)cin>>a[i].F>>a[i].S;
vii dp(n);
REP(i,0,n){
dp[i].resize(a[i].S-a[i].F+1,1);
REP(k,a[i].F,a[i].S+1){
int ps=k-a[i].F;
REP(j,0,i){
int val=0;
if(a[j].F>=k)val=0;
else if(a[j].S<k)val=dp[j].back();
else val=dp[j][k-1-a[i-1].F];
dp[i][ps]+=val;
dp[i][ps]%=M;
}
if(k!=a[i].F){
dp[i][ps]+=dp[i][ps-1];
dp[i][ps]%=M;
}
}
}
int ans=0;
REP(i,0,n){
ans+=dp[i].back();
ans%=M;
}
cout<<ans;
}
