#include <bits/stdc++.h>
#define TASK "askdjkasd"
#define endl '\n'
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define BIT(i,x) (((i)>>(x))&1)
#define FOR(i,a,b) for(int i = (a); i<=(b); i++)
#define FORD(i,a,b) for(int i = (a); i>=(b); i--)
#define all(C) C.begin(), C.end()
using namespace std;
using ll = long long;
using pii = pair<int,int>;
const int INT_LIM = 2147483647;
const ll LL_LIM = 9223372036854775807;
template <typename X> bool minimize(X &x, const X &y) {if (x>y){x = y; return true;}return false;}
template <typename X> bool maximize(X &x, const X &y) {if (x<y){x = y; return true;}return false;}
///------------------------------------------///
const int MOD = 1e9+7;
int pw(int x, int p)
{
int ret = 1;
while (p)
{
if (p&1) ret = 1LL*ret*x%MOD;
x = 1LL*x*x%MOD; p>>=1;
}
return ret;
}
void add(int &x, const int &y)
{
x+=y;
if (x>=MOD) x-=MOD;
}
int inv[505];
int n, m = 0;
int a[505], b[505];
int c[1005];
int f[1005][505];
int nCk[1005][505];
int nCk2[505][505];
void inp()
{
cin >> n;
inv[0] = 1;
FOR(i, 1, n) inv[i] = 1LL*inv[i-1]*i%MOD;
inv[n] = pw(inv[n], MOD-2);
FORD(i, n, 1) inv[i-1] = 1LL*inv[i]*i%MOD;
set<int> tmp;
FOR(i, 1, n)
{
cin >> a[i] >> b[i];
tmp.insert(a[i]);
tmp.insert(b[i]);
}
for (auto i:tmp)
{
c[++m] = i;
}
FOR(i, 1, m)
{
nCk[i][0] = 1;
FOR(j, 1, n)
{
nCk[i][j] = 1LL*nCk[i][j-1]*(c[i]-c[i-1]-j+1)%MOD;
}
// if (i==1) cout << inv[1] << endl;
FOR(j, 1, n) nCk[i][j] = 1LL*nCk[i][j]*inv[j]%MOD;
}
FOR(i, 0, n) FOR(j, 0, i)
{
if (j==0 || j==i) nCk2[i][j] = 1;
else nCk2[i][j] = (nCk2[i-1][j-1]+nCk2[i-1][j])%MOD;
}
}
int calc(int m, int k)
{
if (f[m][k]!=0) return f[m][k];
FOR(i, 0, k) add(f[m][k], 1LL*nCk2[k][i]*nCk[m][i+1]);
return f[m][k];
}
int dp[505][1005];
void solve()
{
FOR(i, 0, m) dp[0][i] = 1;
int ans = 0;
FOR(i, 1, n) FOR(j, 1, m)
{
if (a[i]<=c[j-1]+1 && c[j]<=b[i])
{
// dp[i][j] = c[j]-c[j-1];
int cnt = 0;
FORD(t, i-1, 0)
{
add(dp[i][j], 1LL*dp[t][j-1]*calc(j, cnt)%MOD);
// cout << i << ' ' << j << ' ' << t << ' ' << 1LL*dp[t][j-1]*calc(j, cnt)%MOD << endl;
if (a[t]<=c[j-1]+1 && c[j]<=b[t]) cnt++;
}
// cout << i << ' ' << j << ' ' << dp[i][j] << endl;
}
add(ans, dp[i][j]);
// cout << i << ' ' << j << ' ' << dp[i][j] << endl;
add(dp[i][j], dp[i][j-1]);
}
cout << ans;
}
signed main()
{
///--------------------------///
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
if (fopen(TASK".INP","r")!=NULL)
{
freopen(TASK".INP","r",stdin);
freopen(TASK".OUT","w",stdout);
}
///--------------------------///
int NTEST = 1;
bool codeforces = 0;
if (codeforces) cin >> NTEST;
while (NTEST--)
{
inp();
solve();
}
return 0;
}
///------------------------------------------///
