#include <bits/stdc++.h>
using namespace std;
#define MAX 510
#define all(v) v.begin(), v.end()
#define ln '\n'
#define MOD 1000000007
#define INF 210000000000
#define pb push_back
#define abs(x) (((x)>0)?(x):(-(x)))
#define len(x) ((x).second-(x).first)
typedef long long ll;
vector<ll> dp[MAX], sum[MAX];
ll A[MAX], B[MAX];
set<pair<ll, ll>> s;
int main(void) {
ios::sync_with_stdio(false);
cin.tie(0);
ll N;
cin >> N;
ll i, j, k;
for (i = 1; i <= N; i++) cin >> A[i] >> B[i], dp[i].pb(0), sum[i].pb(0);
for (i = A[1]; i <= B[1]; i++) {
dp[1].pb(1);
sum[1].pb(0);
sum[1][i - A[1] + 1] = (sum[1][i - A[1]] + dp[1][i - A[1] + 1]) % MOD;
}
s.insert({ A[1], 1 });
set<pair<ll, ll>>::iterator it;
for (i = 2; i <= N; i++) {
for (j = A[i]; j <= B[i]; j++) {
dp[i].pb(1), sum[i].pb(0);
for (it = s.begin(); it != s.end(); it++) {
k = it->second;
if (j - A[k] <= 0) break;
dp[i][j - A[i] + 1] += sum[k][min(j - A[k], (ll)(sum[k].size() - 1))];
dp[i][j - A[i] + 1] %= MOD;
}
sum[i][j - A[i] + 1] = (sum[i][j - A[i]] + dp[i][j - A[i] + 1]) % MOD;
s.insert({ A[i], i });
}
}
ll ans = 0;
for (i = 1; i <= N; i++) ans += sum[i][sum[i].size() - 1];
ans %= MOD;
while (ans < 0) ans += MOD;
cout << ans << ln;
return 0;
}
