#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define int ll
const int MOD = 1e9 + 7;
int mod(int x) {
x %= MOD;
if (x < 0)
x += MOD;
return x;
}
void run() {
int n;
cin >> n;
vector<int> a(n), b(n);
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
// assert(a[i] == b[i]);
}
vector<vector<int>> dp(n);
vector<int> dp0(n);
for (int i = 0; i < n; ++i) {
if (i == 0)
dp0[i] = 1;
else
dp0[i] = dp[i - 1].back();
dp[i].resize(b[i] - a[i] + 1);
for (int j = a[i]; j <= b[i]; ++j) {
dp[i][j - a[i]] = 0;
if (j != a[i]) {
dp[i][j - a[i]] += dp[i][j - a[i] - 1];
} else {
dp[i][j - a[i]] += dp0[i];
}
if (i > 0) {
int val = 0;
if (j - 1 >= a[i - 1]) {
if (j - 1 > b[i - 1])
val = dp[i - 1].back();
else
val = dp[i - 1][j - a[i - 1] - 1];
}
else {
val = dp0[i - 1];
}
dp[i][j - a[i]] += val;
} else {
dp[i][j - a[i]] += 1;
}
dp[i][j - a[i]] %= MOD;
}
}
int ans = dp.back().back();
ans--;
ans = mod(ans);
cout << ans << '\n';
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
run();
}
