This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int md = (int)1e9 + 7;
const int N = (int)1e7 + 1;
int main() {
ios::sync_with_stdio(false); cin.tie(nullptr);
int n;
cin >> n;
vector<int> a(n), b(n);
for (int i = 0; i < n; i++) cin >> a[i] >> b[i];
assert(*max_element(b.begin(), b.end()) < N);
vector<int> dp(N);
for (int i = 0; i < n; i++) {
for (int j = b[i]; j >= a[i]; j--) {
dp[j] = (dp[j] + 1) % md;
for (int k = 1; k < j; k++) dp[j] = (dp[j] + dp[k]) % md;
}
}
int sm = 0;
for (auto i : dp) sm = (sm + i) % md;
cout << sm;
}
/*sub1
vector<int> dp(n);
for (int i = 0; i < n; i++) {
dp[i] = 1;
for (int j = 0; j < i; j++) {
if (a[j] < a[i]) dp[i] = (dp[i] + dp[j]) % md;
}
}
int sm = 0;
for (auto i : dp) sm = (sm + i) % md;
cout << sm;
*/
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