#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define int ll
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define PB push_back
#define FS first
#define SD second
#define ary(k) array<int,k>
template<class A,class B> void cmx(A& x, B y) {x=max<A>(x,y);}
template<class A,class B> void cmn(A& x, B y) {x=min<A>(x,y);}
typedef pair<int, int> pii;
typedef vector<int> vi;
const int MM = 1e3+20,MOD = 1e9+7;
typedef int T;
int n; T dp[MM][MM]; vi pts; vector<pii> grps;
pii school[MM]; int lft[MM],rit[MM];
T big_c[MM][MM];
T pre[MM][2][MM],C[MM][MM];
int fpow(int x, int y){
int res = 1;
while(y){
if(y & 1) res = 1ll*res*x%MOD;
x = 1ll*x*x%MOD;
y /= 2;
}
return res;
}
signed main() {
cin.tie(0)->sync_with_stdio(0); cin.exceptions(cin.failbit);
C[0][0] = 1;
rep(i,1,MM){
rep(j,0,i+1){
C[i][j] = C[i-1][j];
if(j) C[i][j] = (C[i][j]+C[i-1][j-1])%MOD;
}
}
cin >> n;
rep(i,1,n+1){
int a,b; cin >> a >> b;
school[i] = {a,b};
pts.PB(a-1);
pts.PB(b);
}
pts.PB(-1);
sort(all(pts));
rep(i,0,sz(pts)-1){
if(pts[i] < pts[i+1]) grps.PB({pts[i]+1,pts[i+1]});
}
int m = sz(grps);
rep(i,1,n+1){
auto[a,b] = school[i];
lft[i] = -1;
rep(j,0,m){
auto[l,r] = grps[j];
if(a <= l && r <= b){
rit[i] = j;
if(!~lft[i]) lft[i] = j;
}
}
assert(~lft[i]);
}
rep(j,0,m){
dp[0][j] = 1;
}
auto fC = [&](int x, int y){
if(x < 0 || x < y || y < 0) return T(0);
return C[x][y];
};
rep(i,1,m){
int len = grps[i].SD-grps[i].FS+1;
T kf = 1,num = 1;
rep(j,1,min(len+1,n+1)){
num = num*(len-j+1)%MOD;
kf = kf*j%MOD;
big_c[i][j] = num*fpow(kf,MOD-2)%MOD;
}
}
assert(m <= 1010);
rep(j,1,m){
rep(p,0,2) rep(num,1,n+1){
T cur = 0;
rep(l,1+p,num+1){
cur = (cur+fC(num-1-p,l-1-p)*big_c[j][l]%MOD)%MOD;
}
pre[j][p][num] = cur;
}
}
T ans = 0;
rep(i,1,n+1){
rep(j,lft[i],rit[i]+1){
// fix first one we use same group j
int num_with = 0;
for(int k = i; k >= 1; k--)if(lft[k] <= j && j <= rit[k]){
num_with++;
dp[i][j] = (dp[i][j]+pre[j][k!=i][num_with]*dp[k-1][j-1]%MOD)%MOD;
}
ans = (ans+dp[i][j])%MOD;
}
// build psa
rep(j,1,m){
dp[i][j] = (dp[i][j]+dp[i][j-1])%MOD;
}
rep(j,0,m){
dp[i][j] = (dp[i][j]+dp[i-1][j])%MOD;
}
}
cout << ans << "\n";
}
