#include <bits/stdc++.h>
#define F first
#define S second
#define P push
#define pb push_back
#define MEM(dp,i) memset(dp,i,sizeof(dp))
#define W while
#define R return
#define C continue
#define SI size()
#define ll long long
#define pll pair<ll,ll>
#define SF(x) scanf("%I64d",&x)
using namespace std;
const long long INF = 2e9;
long long MOD = 1e9+7;
ll n;
ll a[555];
ll b[555];
vector<ll> dp[555];
ll DP(ll x,ll last){
if(x==n)R 1;
if(last>b[x])R DP(x+1,last);
ll p=DP(x+1,last);
last=max(last,a[x]);
ll &ret=dp[x][last-a[x]];
if(ret!=-1)R ret+p;
ret=0;
if(last<=b[x])
ret=DP(x,last+1);
ret%=MOD;
R ret+p;
}
int main(){
cin>>n;
for(int i=0;i<n;i++){
cin>>a[i]>>b[i];
for(int j=a[i];j<=b[i];j++)
dp[i].pb(-1);
}
cout<<(DP(0,1)-1)%MOD;
}
