#include <bits/stdc++.h>
using namespace std;
#define ll long long
int n;
vector<int> a, b;
ll ans = 0;
void dfs(int idx, vector<int>& used, int prev) {
if (idx == n) {
if (!used.empty()) ans++;
return;
}
dfs(idx + 1, used, prev);
for (int x = a[idx]; x <= b[idx]; ++x) {
if (x > prev) {
used.push_back(x);
dfs(idx + 1, used, x);
used.pop_back();
}
}
}
void solve() {
cin >> n;
a.resize(n);
b.resize(n);
for (int i = 0; i < n; ++i)
cin >> a[i] >> b[i];
vector<int> used;
dfs(0, used, -1); // -1: nada previo
cout << ans << '\n';
}
int main() {
ios::sync_with_stdio(0); cin.tie(0);
solve();
}
