#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")
#pragma GCC optimize ("unroll-loops")
#include<bits/stdc++.h>
using namespace std;
const int nmax=1e3+42,mod=1e9+7;
int my_pow(long long a,int b)
{
long long ret=1;
while(b)
{
if(b%2)ret=ret*a%mod;
a=a*a%mod;
b=b/2;
}
return ret;
}
int n;
pair<int,int> inp[nmax];
set< pair<int,int> > seen;
pair<int,int> groups[nmax];
int pointer=0;
int inv[nmax];
int dp[nmax][nmax][2];
int coeff[nmax][nmax];
int rec(int which_number,int last_used_group,bool can_place_zero)
{
if(which_number>n)return 1;//properly chosen
if(last_used_group==pointer)return can_place_zero;//skipped too much
if(dp[which_number][last_used_group][can_place_zero]!=-1)return dp[which_number][last_used_group][can_place_zero];
long long ret=0;
//place zero
if(can_place_zero)ret=(ret+rec(which_number+1,last_used_group,1))%mod;
//place non-zero for other group
ret=(ret+rec(which_number,last_used_group+1,0))%mod;//ignore this group
//place non-zero
if(inp[which_number].first<=groups[last_used_group+1].first&&groups[last_used_group+1].second<=inp[which_number].second)
{
int nums=0;
for(int use=which_number;use<=n;use++)
{
if(inp[use].first<=groups[last_used_group+1].first&&groups[last_used_group+1].second<=inp[use].second)
{
nums++;
ret=(ret+1LL*coeff[last_used_group+1][nums]*rec(use+1,last_used_group+1,1))%mod;
}
//cout<<"which_number= "<<which_number<<" last_used_group= "<<last_used_group<<" use= "<<use<<" mult= "<<coeff[last_used_group+1][nums]<<" can_place_zero= "<<can_place_zero<<" finish= "<<rec(use+1,last_used_group+1,1)<<endl;
}
}
dp[which_number][last_used_group][can_place_zero]=ret;
//cout<<which_number<<" "<<last_used_group<<" "<<can_place_zero<<" -> "<<ret<<endl;
return ret;
}
int C[nmax][nmax];
int ask_C(int n_,int k_)
{
if(0>k_||k_>n_)return 0;
return C[n_][k_];
}
//mod= 1000000007
const long long M=18446743944;//(1<<64)/mod
const unsigned int MX_VAL_INT=4294967295;
const unsigned long long MX_VAL_LONG=18446744073709551615;
const unsigned long long M1=M>>32;
const unsigned long long M2=M&MX_VAL_INT;
int barreet(long long a)
{
unsigned int a1=a>>32;
unsigned int a2=a&MX_VAL_INT;
unsigned long long val_32=M1*a2+M2*a1;
unsigned long long val_0=M2*a2;
unsigned long long q=M1;
q=q*a1;
q=q+(val_32>>32);
val_32=val_32&MX_VAL_INT;
val_32=val_32>>32;
if(MX_VAL_LONG-val_0<val_32)q++;
unsigned int r=a-q*mod;
if(r >= mod) r= r - mod;
//assert(r==a%mod);
return r;
}
/*
typedef unsigned long long ull;
typedef __uint128_t L;
struct FastMod {
ull b, m;
FastMod(ull b) : b(b), m(ull((L(1) << 64) / b)) {}
ull reduce(ull a) {
ull q = (ull)((L(m) * a) >> 64), r = a - q * b;
return r >= b ? r - b : r;
}
};
*/
int main()
{
memset(dp,-1,sizeof(dp));
for(int i=0;i<nmax;i++)
for(int j=0;j<=i;j++)
if(j==0||j==i)C[i][j]=1;
else C[i][j]=(C[i-1][j]+C[i-1][j-1])%mod;
scanf("%i",&n);
for(int i=1;i<nmax;i++)
{
inv[i]=my_pow(i,mod-2);
}
int prv=1e9;
for(int i=1;i<=n;i++)
{
scanf("%i%i",&inp[i].first,&inp[i].second);
seen.insert({inp[i].first,-1});
seen.insert({inp[i].second,0});
prv=min(prv,inp[i].first);
prv=min(prv,inp[i].second);
}
for(auto k:seen)
{
int other=k.first+k.second;
if(prv<=other)
{
pointer++;
groups[pointer]={prv,other};
prv=other+1;
}
}
/*
for(int i=1;i<=n;i++)
for(int j=1;j<=pointer;j++)
{
int le=max(inp[i].first,groups[j].first);
int ri=min(inp[i].second,groups[j].second);
if(le>ri)continue;
assert(le==groups[j].first&&ri==groups[j].second);
}
cout<<"---"<<endl;
for(int i=1;i<=pointer;i++)cout<<groups[i].first<<" "<<groups[i].second<<endl;
*/
for(int which=1;which<=pointer;which++)
for(int nums=1;nums<=n;nums++)
{
int total=groups[which].second-groups[which].first+1;
if(nums==1)coeff[which][1]=total;
else
{
long long coeff_help=total;
for(int zero=nums-2;zero>=0;zero--)
{
if(total<nums-zero)coeff_help=0;
else if(total==nums-zero)coeff_help=1;
else coeff_help=barreet(1LL*barreet(coeff_help*(total-(nums-zero)+1))*inv[nums-zero]);
//cout<<"zero= "<<zero<<" "<<total-(nums-zero)+1<<" , "<<nums-zero<<" actual= "<<inv[nums-zero]<<endl;
//cout<<"zero= "<<zero<<" "<<coeff_help<<" "<<ask_C(total,nums-zero)<<endl;
//if(coeff_help!=ask_C(total,nums-zero))system("pause");
coeff[which][nums]=barreet(coeff[which][nums]+1LL*ask_C(nums-2,zero)*coeff_help);
}
}
//cout<<which<<" "<<nums<<" -> "<<coeff[which][nums]<<endl;
//cout<<"---"<<endl;
}
int out=rec(1,0,1);
out=(out-1+mod)%mod;
printf("%i\n",out);
return 0;
}
