#include<stdio.h>
#include<algorithm>
#define N 509
#define M 1009
#define mod 1000000007
using namespace std;
inline char nc()
{
static char buf[99999],*l,*r;
return l==r&&(r=(l=buf)+fread(buf,1,99999,stdin),l==r)?EOF:*l++;
}
inline void read(int&x)
{
char c=nc();for(;c<'0'||'9'<c;c=nc());
for(x=0;'0'<=c&&c<='9';x=(x<<3)+(x<<1)+(c^48),c=nc());
}
int n,m,a[N],b[N],lsh[M],f[N][M],inv[N],ans;
inline long long ksm(long long a,int b)
{
long long ans=1;
for(;b;b>>=1,a*=a,a%=mod)if(b&1)ans*=a,ans%=mod;
return ans;
}
main()
{
read(n);
for(int i=1;i<=n;inv[i]=ksm(i,mod-2),++i)
read(a[i]),read(b[i]),lsh[m++]=a[i],lsh[m++]=b[i]+1;
lsh[m++]=0;lsh[m++]=1000000001;
sort(lsh,lsh+m);m=unique(lsh,lsh+m)-lsh;--m;
for(int i=0;i<m;f[0][i++]=1);
for(int i=1;i<=n;++i)
{
for(int l=lower_bound(lsh,lsh+m,a[i])-lsh,r=upper_bound(lsh,lsh+m,b[i])-lsh
;l<r;++l)
{
for(int j=i-1,k=lsh[l+1]-lsh[l],cnt=1;j>=0;--j)
{
f[i][l]=(f[i][l]+(long long)(k)*f[j][l-1])%mod;
if(a[j]<=lsh[l]&&lsh[l]<=b[j])++cnt,
k=k*(long long)(lsh[l+1]-lsh[l]+cnt-1)%mod*inv[cnt]%mod;
}
}
for(int j=1;j<m;++j)f[i][j]+=f[i][j-1]-mod,f[i][j]>>31&&(f[i][j]+=mod);
ans+=f[i][m-1]-mod,ans>>31&&(ans+=mod);
}
printf("%d",ans);
}
