Language: C++

#pragma region includes, macros
#include <iostream>
#include <algorithm>
#include <functional>
#include <string>
#include <vector>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <map>
#include <set>
#include <list>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <limits>

using namespace std;

typedef int64_t i64;
typedef pair<i64, i64> P;

static const i64 MOD = 1000000007;

//int dx[5] = {-1,0,0,0,1}, dy[5] = {0,-1,0,1,0};
//int dx[8] = {-1,0,1,1,1,0,-1,-1}, dy[8] = {1,1,1,0,-1,-1,-1,0};
//int dx[9] = {-1,0,1,1,1,0,-1,-1,0}, dy[9] = {1,1,1,0,-1,-1,-1,0,0};

struct edge {
    i64 from, to, cost;
    edge(i64 to, i64 cost) : from(-1), to(to), cost(cost) {}
    edge(i64 src, i64 to, i64 cost) : from(src), to(to), cost(cost) {}
};

// http://beet-aizu.hatenablog.com/entry/2018/04/08/145516
template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }

template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type
fill_v(T& t, const V& v) { t = v; }

template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type
fill_v(T& t, const V& v) {
    for (auto& e : t) fill_v(e, v);
}
//

#pragma endregion

int dx[4] = { 0,1,0,-1 }, dy[4] = { -1,0,1,0 };

int main() {
    i64 n, m;
    cin >> n >> m;
    i64 al = 1, ar = n;
    for (int i = 0; i < m; ++i) {
        i64 l, r;
        cin >> l >> r;
        al = max(l, al);
        ar = min(r, ar);
    }
    cout << max(0LL, ar - al + 1) << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:71:16: error: no matching function for call to 'max(long long int, i64)'
   71 |     cout << max(0LL, ar - al + 1) << endl;
      |             ~~~^~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:51,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:71:16: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'i64' {aka 'long int'})
   71 |     cout << max(0LL, ar - al + 1) << endl;
      |             ~~~^~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61,
                 from a.cc:3:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:71:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   71 |     cout << max(0LL, ar - al + 1) << endl;
      |             ~~~^~~~~~~~~~~~~~~~~~