#include <cstdio>
#include <cstring>
#include <vector>
#include <cstring>
#include <algorithm>
#define X first
#define Y second
#define PB push_back
using namespace std;
typedef long long ll;
const int N = 1005;
const int MOD = 1e9 + 7;
inline int add(const int &A, const int &B){
if(A + B >= MOD) return A + B - MOD;
return A + B;
}
inline int mul(const int &A, const int &B){
return (ll)A * B % MOD;
}
inline int sub(const int &A, const int &B){
if(A - B < 0) return A - B + MOD;
return A - B;
}
inline int eks(const int &A, int B){
int ans = 1, bs = A;
for(;B;B >>= 1){
if(B & 1)
ans = mul(ans, bs);
bs = mul(bs, bs);
}
return ans;
}
int n, inv[N], fak[N];
int ch[N][N], L[N], R[N], b_L[N], b_R[N], m, in[N][N], ch2[N][N], pos[N][N], dp[N][N];
vector < int > v;
void precompute(){
fak[0] = 1; inv[0] = 1;
for(int i = 1;i < N;i++){
fak[i] = mul(i, fak[i - 1]);
inv[i] = eks(fak[i], MOD - 2);
}
for(int i = 0;i < N;i++){
ch[i][i] = 1; ch[i][0] = 1;
}
for(int i = 1;i < N;i++){
for(int j = 1;j < i;j++){
ch[i][j] = add(ch[i - 1][j], ch[i - 1][j - 1]);
}
}
}
int f(int bl, int i){
if(bl == m) return 1;
if(dp[bl][i] != -1) return dp[bl][i];
int ret = f(bl + 1, i);
int cnt = 0;
for(int j = i;j < n;j++){
cnt += in[j][bl];
if(in[j][bl]){
ret = add(ret, mul(f(bl + 1, j + 1), pos[bl][cnt]));
}
}
return dp[bl][i] = ret;
}
int brute(int i,int lst){
if(i == n) return 1;
int ret = brute(i + 1, lst);
for(int j = max(L[i], lst + 1);j <= R[i];j++)
ret += brute(i + 1, j);
return ret;
}
int main(){
memset(dp, -1, sizeof(dp));
precompute();
scanf("%d", &n);
for(int i = 0;i < n;i++){
scanf("%d%d", L + i, R + i);
v.PB(L[i]); v.PB(R[i] + 1);
}
sort(v.begin(), v.end());
v.erase(unique(v.begin(), v.end()), v.end());
m = v.size() - 1;
for(int i = 0;i < m;i++){
b_L[i] = v[i]; b_R[i] = v[i + 1] - 1;
//printf("BLOK %d : %d %d\n", i, b_L[i], b_R[i]);
}
for(int i = 0;i < n;i++){
for(int j = 0;j < m;j++){
if(L[i] <= b_L[j] && b_R[j] <= R[i])
in[i][j] = 1;
}
}
for(int i = 0;i < m;i++){
int len = b_R[i] - b_L[i] + 1;
int cur = len; ch2[i][0] = 1;
for(int j = 1;j <= n;j++){
ch2[i][j] = mul(cur, inv[j]);
//printf("%d povrh %d = %d\n", len, j, ch2[i][j]);
cur = mul(cur, len - j);
}
}
for(int i = 0;i < m;i++){
for(int j = 1;j <= n;j++){
for(int k = 0;k < j;k++){
pos[i][j] = add(pos[i][j], mul(ch2[i][k + 1], ch[j - 1][k]));
}
//printf("pos[%d][%d] = %d\n", i, j, pos[i][j]);
}
}
printf("%d\n", sub(f(0,0), 1));
// printf("%d\n", sub(brute(0,0), 1));
}
