#include <iostream>
#include <algorithm>
#define ll long long
using namespace std;
const ll MD = 1e9 + 7;
ll dp[501][2002], pf[501][2002], pre[2002][501];
int n, a[501], b[501], c[2002], sz = 1;
inline ll pw(ll b, ll e)
{
e = (e + MD - 1) % (MD - 1);
ll t = 1;
while (e)
{
if (e & 1) {t = (t * b) % MD;}
b = (b * b) % MD; e >>= 1;
}
return t;
}
int main()
{
cin >> n;
for (int i = 0; i < n; i++)
{
cin >> a[i] >> b[i];
c[sz++] = a[i];
c[sz++] = a[i] - 1;
c[sz++] = b[i] + 1;
c[sz++] = b[i];
}
sort(c, c + sz);
sz = unique(c, c + sz) - c;
for (int i = 1; i < sz; i++)
{
ll cur = 1;
for (int j = 0; j <= n; j++)
{
pre[i][j] = cur;
cur = (cur * (c[i] - c[i - 1] + j)) % MD;
cur = (cur * pw(j + 1, -1)) % MD;
}
}
dp[0][0] = 1;
pf[0][0] = 1;
for (int j = 1; j < sz; j++) {pf[0][j] = pf[0][j - 1];}
for (int i = 1; i <= n; i++)
{
pf[i][0] = dp[i][0] = 1;
for (int j = 1; j < sz; j++)
{
int kk = 0;
for (int k = i - 1; k >= 0; k--)
{
kk += (a[k] <= c[j - 1] + 1) && (c[j] <= b[k]);
if (kk && ((a[k] <= c[j - 1] + 1) && (c[j] <= b[k])))
{
dp[i][j] = (dp[i][j] + pf[k][j - 1] * pre[j][kk] % MD) % MD;
}
}
// cout << "DP " << i << " " << j << " " << dp[i][j] << "\n";
pf[i][j] = (pf[i][j - 1] + dp[i][j]) % MD;
}
}
ll res = 0;
for (int j = 1; j < sz; j++) res = (res + dp[n][j]) % MD;
cout << res << "\n";
return 0;
}
