//by szh
#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pii pair<int,int>
#define pll pair<long long,long long>
#define pb push_back
#define debug(x) cerr<<#x<<"="<<x<<endl
#define pq priority_queue
#define inf 0x3f
#define rep(i,a,b) for (int i=a;i<(b);i++)
#define MP make_pair
#define SZ(x) (int(x.size()))
#define ll long long
#define mod 1000000007
#define ALL(x) x.begin(),x.end()
void inc(int &a,int b) {a=(a+b)%mod;}
void dec(int &a,int b) {a=(a-b+mod)%mod;}
int lowbit(int x) {return x&(-x);}
ll p0w(ll base,ll p) {ll ret=1;while(p>0){if (p%2ll==1ll) ret=ret*base%mod;base=base*base%mod;p/=2ll;}return ret;}
const int maxn=1e3+10;
int n;
int f[2][maxn][maxn];
int a[maxn],b[maxn];
map <int,int> mp;
int pm[maxn];
ll inv[maxn];
int sum[maxn];
int main() {
// freopen("input.txt","r",stdin);
std::ios::sync_with_stdio(false);cin.tie();
cin>>n;
rep(i,1,maxn) inv[i]=p0w(i,mod-2);
mp[0]=1;
rep(i,1,n+1) cin>>a[i]>>b[i],a[i]--,mp[a[i]]=mp[b[i]]=1;
int tot=0;
for (auto &it:mp) it.se=tot,pm[tot++]=it.fi;
int lst=0,cur=1;
f[lst][0][0]=1;
rep(i,1,n+1) {
memset(sum,0,sizeof(sum));
memset(f[cur],0,sizeof(f[cur]));
rep(j,0,tot)
rep(k,0,i) {
if (f[lst][j][k]==0) continue;
//doesn't choose
inc(f[cur][j][k],f[lst][j][k]);
inc(sum[j],f[lst][j][k]);
// cout<<i-1<<" "<<j<<" "<<k<<" "<<f[lst][j][k]<<endl;
}
// debug(sum[0]),debug(sum[1]),debug(sum[2]);
rep(j,mp[a[i]]+1,mp[b[i]]+1) {
rep(k,0,i) {
//choose from the same segment
if (pm[j]-pm[j-1]>=k+1) inc(f[cur][j][k+1],1ll*f[lst][j][k]*(pm[j]-pm[j-1]-k)%mod*inv[k+1]%mod);
}
}
rep(j,1,tot) inc(sum[j],sum[j-1]);
// debug(sum[1]),debug(sum[2]),debug(sum[3]);
// debug(a[i]),debug(b[i]),debug(mp[a[i]]),debug(mp[b[i]]);
rep(j,mp[a[i]],mp[b[i]]) {
//start from a new segment
inc(f[cur][j+1][1],1ll*sum[j]*(pm[j+1]-pm[j])%mod);
}
swap(lst,cur);
}
int ans=0;
rep(i,1,tot)
rep(j,1,n+1) inc(ans,f[lst][i][j]);
cout<<ans<<endl;
return 0;
}
