#include <cstdio>
#include <algorithm>
const int md = 1000000007;
inline int add(int a, int b)
{
a += b;
if (a >= md) a -= md;
return a;
}
inline int sub(int a, int b)
{
a -= b;
if (a < 0) a += md;
return a;
}
inline int mul(int a, int b)
{
return (long long)a * b % md;
}
int po(int a, int b)
{
int r = 1;
while (b) {
if (b & 1) r = mul(r, a);
a = mul(a, a);
b >>= 1;
}
return r;
}
inline int inv(int a)
{
return po(a, md - 2);
}
inline int di(int a, int b)
{
return mul(a, inv(b));
}
const int N = 505;
int n, d[N << 1], l[N], r[N], a[N << 1], p[N << 1][N], amt[N << 1], ncr[N << 1][N];
int main()
{
scanf("%d", &n);
for (int i = 0; i < n; ++i) {
scanf("%d%d", l + i, r + i);
a[i << 1] = l[i];
a[i << 1 | 1] = r[i] + 1;
}
std::sort(a, a + n * 2);
int len = std::unique(a, a + n * 2) - a;
d[0] = 1;
for (int i = 0; i < n; ++i) {
for (int j = len - 1; j >= 1; --j) if (l[i] <= a[j - 1] && r[i] >= a[j] - 1) {
if (!amt[j]) ncr[j][0] = a[j] - a[j - 1];
else ncr[j][amt[j]] = di(mul(ncr[j][amt[j] - 1], ncr[j][0] - amt[j]), amt[j] + 1);
for (int k = amt[j]; k > 0; --k) {
p[j][k] = add(p[j][k], p[j][k - 1]);
d[j] = add(d[j], mul(p[j][k - 1], ncr[j][k]));
}
for (int k = 0; k < j; ++k) {
p[j][0] = add(p[j][0], d[k]);
d[j] = add(d[j], mul(ncr[j][0], d[k]));
}
++amt[j];
}
}
int ans = 0;
for (int i = 1; i < len; ++i) ans = add(ans, d[i]);
printf("%d\n", ans);
return 0;
}
