Stickers on the wall (Easy)

  #include <bits/stdc++.h>
  using namespace std;

  #define cin(vec) for(auto& i : vec) cin >> i
  #define cin_2d(vec, n, m) for(int i = 0; i < n; i++) for(int j = 0; j < m && cin >> vec[i][j]; j++);
  #define cout(vec) for(auto& i : vec) cout << i << " "; cout << "\n";
  #define cout_map(mp) for(auto& [f, s] : mp) cout << f << "  " << s << "\n";
  #define loop(a, b, c) for(int i = a ; i < (b); i += c)
  #define Ceil(n, m) ((n / m) + (n % m ? 1 : 0))
  #define all(vec) vec.begin(),vec.end()
  #define rall(vec) vec.rbegin(),vec.rend()
  #define sz size()
  #define fi first
  #define se second
  #define Pair pair <int,int>
  #define ll long long
  #define ull unsigned long long
  #define Mod  1000'000'007
  #define INF 2000'000'000
  #define PI 3.14159265359

  void Code_Crush(){
    ios_base::sync_with_stdio(false);   cin.tie(nullptr);   cout.tie(nullptr);
    #ifndef ONLINE_JUDGE
      freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
    #endif
  }

  int main(){
    Code_Crush();
    int n, m, q;                     cin >> n >> m >> q;
    vector <ll> points(n + 2);
    while(q--){
      int x1, x2;            cin >> x1 >> x2;
      points[min(x1, x2)]++, points[max(x1, x2) + 1]--;
    }
    for(int i = 1; i <= n; i++){
      points[i] += points[i - 1];
    }
    ll count = 0;
    for(int i = 1; i <= n; i++){
        count += !points[i];
    }
    cout << count;
    return 0;
  }