#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define ins insert
#define fi first
#define se second
#define ld long double
#define ALL(x) (x).begin(), (x).end()
#define MASK(x) (1ULL << (x))
#define BIT(x, k) ((x) >> (k) & 1)
#define TIME (1.0 * clock() / CLOCKS_PER_SEC)
template<typename T1, typename T2> bool maximize(T1 &x, const T2 &y){
if (x < y){
x = y;
return 1;
}
return 0;
}
template<typename T1, typename T2> bool minimize(T1 &x, const T2 &y){
if (x > y){
x = y;
return 1;
}
return 0;
}
bool ST_ALLOC;
#define file "BOAT"
void fastio(){
if (fopen(file".INP", "r")){
freopen(file".INP", "r", stdin);
freopen(file".OUT", "w", stdout);
}
}
const int maxn = 5e2 + 9;
const int mod = 1e9 + 7;
void add(int &a, const int &b){
a += b;
if (a >= mod)
a -= mod;
}
void sub(int &a, const int &b){
a -= b;
if (a < 0)
a += mod;
}
int mul(const int &a, const int &b){
return (1ll * a * b) % mod;
}
int binpow(int a, int b){
int res = 1;
while (b > 0){
if (b & 1)
res = mul(res, a);
a = mul(a, a);
b >>= 1;
}
return res;
}
int n;
int a[maxn];
int b[maxn];
int fiv[maxn];
int fact[maxn];
int L[maxn << 1];
int R[maxn << 1];
int maxR[maxn << 1];
int dp[maxn][maxn << 1];
vector<int> com;
priority_queue<int, vector<int>> pq;
int getID(int val){
return lower_bound(ALL(com), val) - com.begin() + 1;
}
bool EN_ALLOC;
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
fastio();
cin >> n;
for(int i = 1; i <= n; ++i){
cin >> a[i] >> b[i];
com.pb(a[i]);
com.pb(b[i]);
}
sort(ALL(com));
com.erase(unique(ALL(com)), com.end());
for(int i = 1; i <= n; ++i)
maximize(maxR[getID(a[i])], b[i]);
int SIZE = com.size();
for(int i = 1; i <= SIZE; ++i){
int id = getID(com[i - 1]);
if (maxR[id] != 0)
pq.push(maxR[id]);
if (pq.size() && (int)pq.top() > com[i - 1])
L[i] = com[i - 1], R[i] = com[i] - 1;
else
L[i] = R[i] = com[i - 1];
}
fact[0] = fiv[0] = 1;
for(int i = 1; i <= n; ++i)
fact[i] = (1ll * fact[i - 1] * i) % mod;
fiv[n] = binpow(fact[n], mod - 2);
for(int i = n - 1; i >= 1; --i)
fiv[i] = (1ll * (i + 1) * fiv[i + 1]) % mod;
for(int i = 0; i <= SIZE; ++i)
dp[0][i] = 1;
for(int i = 1; i <= n; ++i){
dp[i][0] = 1;
for(int j = 1; j <= SIZE; ++j){
dp[i][j] = dp[i - 1][j]; //Khong chon i
add(dp[i][j],
dp[i][j - 1]); //Ghep i vao nhung doan nho hon
sub(dp[i][j],
dp[i - 1][j - 1]);
int way = 1;
int len = R[j] - L[j] + 1;
for(int pre = i; pre >= 1; --pre){
if ((i - pre + 1) > (R[j] - L[j] + 1))
break;
if (L[j] < a[pre] || R[j] > b[pre])
break;
//C(len, cnt) = (len - cnt + 1)...len/cnt!
//S(len, cnt) = sigma(C(len, x) * C(cnt, x)) = C(len + cnt, cnt)
// = (len + 1)...(len + cnt)/cnt!
if (dp[pre - 1][j - 1] == 0)
continue;
int total = mul(way, fiv[i - pre]);
add(dp[i][j],
mul(dp[pre - 1][j - 1], total));
way = mul(way, len + i - pre + 1);
}
}
}
cout << (dp[n][SIZE] - 1 + mod) % mod << '\n';
cerr << "Time ran : " << TIME << "s\n";
cerr << "Static memory used : " << fixed << setprecision(2) << (((&EN_ALLOC) - (&ST_ALLOC)) / (1.0l * 1024 * 1024)) << "mb\n";
return 0;
}
