将醒着的时刻和睡着的时刻标记一下即可。

#include <bits/stdc++.h>

using i64 = long long;
using u32 = unsigned;
using u64 = unsigned long long;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

 	int n;
 	std::cin >> n;

 	std::vector<int> s(n + 1, 1);
 	for (int i = 0; i < 6; ++i) {
 		int a, b;
 		std::cin >> a >> b;
 		for (int j = a; j <= std::min(b + 3, n); ++j) {
 			s[j] = 0;
 		}
 	}

 	int ans = 0;
 	for (int i = 0; i <= n; ++i) {
 		ans += s[i];
 	}

 	std::cout << ans;

    return 0;
}