Language: C++

#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <cmath>

#pragma GCC optimize ("-O3")
#define rep(i, initial_value, max_value) for (uint64_t i{initial_value}; i < max_value; ++i)
#define fore(i, a) for(auto &i:a)
#define each(i, c) \
    for( \
        __typeof((c).begin()) i{(c).begin()}, __typeof((c).end()) end{(c).end()}; \
        i != end; \
        ++i \
    )
#define dbg(x) cerr << __LINE__ << ": " << #x << " = " << (x) << endl
#define all(x) (x).begin(),(x).end()

using namespace std; void _main(); int main() { cin.tie(0); ios::sync_with_stdio(false); _main(); }
using i64 = int64_t; using i32 = int32_t; using u64 = uint64_t; using u32 = uint32_t;
template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }
template<class T>bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }

// ===

void _main() {
  u64 n;
  u64 m;

  cin >> n >> m;

  u64 L[m];
  u64 R[m];

  rep(i, 0, m) cin >> L[i] >> R[i];

  sort(L, L + m, greater<u64>());
  sort(R, R + m);

  u64 ans = R[0] - L[0];
  chmax(ans, 0ull);

  cout << ans << endl;
}

Compiler output:
a.cc:20:55: error: 'uint64_t' does not name a type
   20 | using i64 = int64_t; using i32 = int32_t; using u64 = uint64_t; using u32 = uint32_t;
      |                                                       ^~~~~~~~
a.cc:6:1: note: 'uint64_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
    5 | #include <cmath>
  +++ |+#include <cstdint>
    6 | 
a.cc:20:77: error: 'uint32_t' does not name a type
   20 | using i64 = int64_t; using i32 = int32_t; using u64 = uint64_t; using u32 = uint32_t;
      |                                                                             ^~~~~~~~
a.cc:20:77: note: 'uint32_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
a.cc: In function 'void _main()':
a.cc:27:3: error: 'u64' was not declared in this scope; did you mean 'i64'?
   27 |   u64 n;
      |   ^~~
      |   i64
a.cc:28:6: error: expected ';' before 'm'
   28 |   u64 m;
      |      ^~
      |      ;
a.cc:30:10: error: 'n' was not declared in this scope; did you mean 'yn'?
   30 |   cin >> n >> m;
      |          ^
      |          yn
a.cc:30:15: error: 'm' was not declared in this scope; did you mean 'tm'?
   30 |   cin >> n >> m;
      |               ^
      |               tm
a.cc:32:6: error: expected ';' before 'L'
   32 |   u64 L[m];
      |      ^~
      |      ;
a.cc:33:6: error: expected ';' before 'R'
   33 |   u64 R[m];
      |      ^~
      |      ;
a.cc:8:47: error: 'uint64_t' was not declared in this scope
    8 | #define rep(i, initial_value, max_value) for (uint64_t i{initial_value}; i < max_value; ++i)
      |                                               ^~~~~~~~
a.cc:35:3: note: in expansion of macro 'rep'
   35 |   rep(i, 0, m) cin >> L[i] >> R[i];
      |   ^~~
a.cc:8:47: note: 'uint64_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
    8 | #define rep(i, initial_value, max_value) for (uint64_t i{initial_value}; i < max_value; ++i)
      |                                               ^~~~~~~~
a.cc:35:3: note: in expansion of macro 'rep'
   35 |   rep(i, 0, m) cin >> L[i] >> R[i];
      |   ^~~
a.cc:35:7: error: 'i' was not declared in this scope
   35 |   rep(i, 0, m) cin >> L[i] >> R[i];
      |       ^
a.cc:8:74: note: in definition of macro 'rep'
    8 | #define rep(i, initial_value, max_value) for (uint64_t i{initial_value}; i < max_value; ++i)
      |                                                                          ^
a.cc:8:87: error: expected ')' before ';' token
    8 | #define rep(i, initial_value, max_value) for (uint64_t i{initial_value}; i < max_value; ++i)
      |                                              ~                                        ^
a.cc:35:3: note: in expansion of macro 'rep'
   35 |   rep(i, 0, m) cin >> L[i] >> R[i];
      |   ^~~
a.cc:35:7: error: 'i' was not declared in this scope
   35 |   rep(i, 0, m) cin >> L[i] >> R[i];
      |       ^
a.cc:8:91: note: in definition of macro 'rep'
    8 | #define rep(i, initial_value, max_value) for (uint64_t i{initial_value}; i < max_value; ++i)
      |                                                                                           ^
a.cc:37:8: error: 'L' was not declared in this scope
   37 |   sort(L, L + m, greater<u64>());
      |        ^
a.cc:37:3: error: 'sort' was not declared in this scope; did you mean 'sqrt'?
   37 |   sort(L, L + m, greater<u64>());
      |   ^~~~
      |   sqrt
a.cc:38:8: error: 'R' was not declared in this scope
   38 |   sort(R, R + m);
      |        ^
a.cc:40:6: error: expected ';' before 'ans'
   40 |   u64 ans = R[0] - L[0];
      |      ^~~~
      |      ;
a.cc:41:9: error: 'ans' was not declared in this scope; did you mean 'abs'?
   41 |   chmax(ans, 0ull);
      |         ^~~
      |         abs