Problem p03391 (C++)

Buggy submission (status: Time Limit Exceeded):
#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#define _SILENCE_CXX17_RESULT_OF_DEPRECATION_WARNING
#include "bits/stdc++.h"
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define FOR(i, m, n) for (int i = (m); i < (n); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; --i)
#define rfor(i, m, n) for (int i = (m); i >= (n); --i)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define range_it(a, l, r) (a).begin() + (l), (a).begin() + (r)

using namespace std;
using LL = long long;
using ld = long double;
using VB = vector<bool>;
using VVB = vector<VB>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<LL>;
using VVL = vector<VL>;
using VS = vector<string>;
using VD = vector<double>;
using PII = pair<int, int>;
using VP = vector<PII>;
using PLL = pair<LL, LL>;
using VPL = vector<PLL>;
template <class T> using Grid = vector<vector<T>>;
template <class T> using PQ = priority_queue<T>;
template <class T> using PQS = priority_queue<T, vector<T>, greater<T>>;
constexpr int inf = (int)1e9;
constexpr LL inf_ll = (LL)1e18, MOD = 1000000007;
constexpr ld PI = M_PI, EPS = 1e-12;

template <class T> inline void Sort(T &a) noexcept { sort(all(a)); }
template <class T> inline void RSort(T &a) noexcept { sort(rall(a)); }
template <class T> inline void Reverse(T &a) noexcept { reverse(all(a)); }
template <class T> inline void Unique(T &a) noexcept {
  a.erase(unique(all(a)), a.end());
}
template <class T> inline T Sorted(T a) noexcept {
  Sort(a);
  return a;
}
template <class T> inline T RSorted(T a) noexcept {
  RSort(a);
  return a;
}
template <class T> inline T Reversed(T a) noexcept {
  Reverse(a);
  return a;
}
template <class T> inline T Uniqued(T a) noexcept {
  Unique(a);
  return a;
}
template <class T> inline auto Max(const T &a) noexcept {
  return *max_element(all(a));
}
template <class T> inline auto Min(const T &a) noexcept {
  return *min_element(all(a));
}
template <class T> inline int MaxPos(const T &a) noexcept {
  return max_element(all(a)) - a.begin();
}
template <class T> inline int MinPos(const T &a) noexcept {
  return min_element(all(a)) - a.begin();
}
template <class T, class U> inline int Count(const T &a, const U &v) noexcept {
  return count(all(a), v);
}
template <class T, class U> inline int Find(const T &a, const U &v) noexcept {
  return find(all(a), v) - a.begin();
}
template <class T, class U> inline U Sum(const T &a, const U &v) noexcept {
  return accumulate(all(a), v);
}
template <class T, class U> inline int Lower(const T &a, const U &v) noexcept {
  return lower_bound(all(a), v) - a.begin();
}
template <class T, class U> inline int Upper(const T &a, const U &v) noexcept {
  return upper_bound(all(a), v) - a.begin();
}
template <class T, class P> inline void RemoveIf(T &a, P f) noexcept {
  a.erase(remove_if(all(a), f), a.end());
}
template <class T> inline T Age(T n, T m) noexcept { return (n + m - 1) / m; }
template <class T> inline T Age2(T n, T m) noexcept { return Age(n, m) * m; }
template <class T> inline T Tri(T n) noexcept {
  return (n & 1) ? (n + 1) / 2 * n : n / 2 * (n + 1);
}
template <class T = long long> inline T BIT(int b) noexcept {
  return T{1} << b;
}
template <class T> inline T Gcd(T n, T m) noexcept {
  return m ? Gcd(m, n % m) : n;
}
template <class T> inline T Lcm(T n, T m) noexcept { return n / Gcd(n, m) * m; }
template <class T> inline T Pow(T a, T n) noexcept {
  T r = 1;
  while (n > 0) {
    if (n & 1)
      r *= a;
    a *= a;
    n /= 2;
  }
  return r;
}
template <class T> inline T Powmod(T a, T n, T m = MOD) noexcept {
  T r = 1;
  while (n > 0) {
    if (n & 1)
      r = r * a % m, n--;
    else
      a = a * a % m, n /= 2;
  }
  return r;
}
template <class T> inline bool chmax(T &a, const T &b) noexcept {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, const T &b) noexcept {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool inRange(const T &v, const T &min, const T &max) noexcept {
  return min <= v && v <= max;
}
inline string operator*(string s, int n) noexcept {
  string ret;
  rep(i, n) ret += s;
  return ret;
}

// --- input --- //
#if defined(_WIN32) || defined(ONLINE_JUDGE)
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#endif
inline int gc() noexcept { return getchar_unlocked(); }
template <class T> inline void InputF(T &v) noexcept { cin >> v; }
inline void InputF(char &v) noexcept {
  while (isspace(v = gc()))
    ;
}
inline void InputF(string &v) noexcept {
  char c;
  for (InputF(c); !isspace(c); c = gc())
    v += c;
}
inline void InputF(int &v) noexcept {
  bool neg = false;
  v = 0;
  char c;
  InputF(c);
  if (c == '-') {
    neg = true;
    c = gc();
  }
  for (; isdigit(c); c = gc())
    v = v * 10 + (c - '0');
  if (neg)
    v = -v;
}
inline void InputF(long long &v) noexcept {
  bool neg = false;
  v = 0;
  char c;
  InputF(c);
  if (c == '-') {
    neg = true;
    c = gc();
  }
  for (; isdigit(c); c = gc())
    v = v * 10 + (c - '0');
  if (neg)
    v = -v;
}
inline void InputF(double &v) noexcept {
  double dp = 1;
  bool neg = false, adp = false;
  v = 0;
  char c;
  InputF(c);
  if (c == '-') {
    neg = true;
    c = gc();
  }
  for (; isdigit(c) || c == '.'; c = gc()) {
    if (c == '.')
      adp = true;
    else if (adp)
      v += (c - '0') * (dp *= 0.1);
    else
      v = v * 10 + (c - '0');
  }
  if (neg)
    v = -v;
}
template <class T, class U> inline void InputF(pair<T, U> &v) noexcept {
  InputF(v.first);
  InputF(v.second);
}
template <class T> inline void InputF(vector<T> &v) noexcept {
  for (auto &e : v)
    InputF(e);
}
template <class T> inline T InputF() {
  T v;
  InputF(v);
  return v;
}
struct InputV {
  int n, m;
  InputV(int N) : n(N), m(0) {}
  InputV(pair<int, int> N) : n(N.first), m(N.second) {}
  template <class T> operator vector<T>() noexcept {
    vector<T> v(n);
    InputF(v);
    return v;
  }
  template <class T> operator vector<vector<T>>() noexcept {
    vector<vector<T>> v(n, vector<T>(m));
    InputF(v);
    return v;
  }
};
struct Input {
  template <class T> operator T() noexcept { return InputF<T>(); }
  int operator--(int) {
    int v;
    InputF(v);
    v--;
    return v;
  }
  InputV operator[](int n) noexcept { return InputV(n); }
  InputV operator[](pair<int, int> n) noexcept { return InputV(n); }
  void operator()() {}
  template <class H, class... T> void operator()(H &&h, T &&...t) {
    InputF(h);
    operator()(forward<T>(t)...);
  }
  template <class T, size_t W> array<vector<T>, W> get(int H) {
    array<vector<T>, W> ret;
    rep(i, H) rep(j, W) {
      T x = *this;
      ret[j].push_back(x);
    }
    return ret;
  }
} in;
#define input(type) InputF<type>()

// --- output --- //
struct BoolStr {
  const char *t, *f;
  BoolStr(const char *_t, const char *_f) : t(_t), f(_f) {}
} Yes("Yes", "No"), yes("yes", "no"), YES("YES", "NO"), Int("1", "0");
struct DivStr {
  const char *d, *l;
  DivStr(const char *_d, const char *_l) : d(_d), l(_l) {}
} spc(" ", "\n"), no_spc("", "\n"), end_line("\n", "\n"), comma(",", "\n"),
    no_endl(" ", "");
class Output {
  BoolStr B{Yes};
  DivStr D{spc};
  bool isPrint = true;
  void p(double v) { printf("%.20f", v); }
  void p(long double v) { printf("%.20Lf", v); }
  void p(int v) { printf("%d", v); }
  void p(LL v) { printf("%lld", v); }
  void p(char v) { putchar(v); }
  void p(bool v) { printf("%s", v ? B.t : B.f); }
  template <class T> void p(const T &v) { cout << v; }
  template <class T, class U> void p(const pair<T, U> &v) {
    p(v.first);
    printf("%s", D.d);
    p(v.second);
  }
  template <class T> void p(const vector<T> &v) {
    rep(i, sz(v)) {
      if (i)
        printf("%s", D.d);
      p(v[i]);
    }
  }
  template <class T> void p(const vector<vector<T>> &v) {
    rep(i, sz(v)) {
      if (i)
        printf("%s", D.l);
      p(v[i]);
    }
  }
  void p(const BoolStr &v) {
    B = v;
    isPrint = false;
  }
  void p(const DivStr &v) {
    D = v;
    isPrint = false;
  }

public:
  Output &operator()() {
    printf("%s", D.l);
    return *this;
  }
  template <class H> Output &operator()(H &&h) {
    p(h);
    if (isPrint)
      printf("%s", D.l);
    isPrint = true;
    return *this;
  }
  template <class H, class... T> Output &operator()(H &&h, T &&...t) {
    p(h);
    if (isPrint)
      printf("%s", D.d);
    isPrint = true;
    return operator()(forward<T>(t)...);
  }
  template <class... T> void exit(T &&...t) {
    operator()(forward<T>(t)...);
    std::exit(EXIT_SUCCESS);
  }
  Output &flush() {
    cout.flush();
    return *this;
  }
} out;

// --- dump --- //
#if __has_include("dump.hpp")
#include "dump.hpp"
#else
#define dump(...) (void(0))
#endif

template <class F> auto MakeVector(size_t size, F f) {
  vector<decay_t<result_of_t<F(size_t)>>> res(size);
  for (size_t i = 0; i < size; ++i)
    res[i] = f(i);
  return res;
}
template <class T> T Slice(const T &v, size_t i, size_t len) {
  return i < v.size()
             ? vector<T>(v.begin() + i, v.begin() + min(i + len, v.size()))
             : vector<T>();
}
template <class T, class F> void Each(T &v, F f) {
  for (auto &e : v)
    f(e);
}
template <class T, class F> auto Map(const T &v, F f) {
  vector<decay_t<result_of_t<F(typename T::value_type)>>> res(v.size());
  size_t i = 0;
  for (const auto &e : v)
    res[i++] = f(e);
  return res;
}
template <class T, class F> auto MapIndex(const T &v, F f) {
  vector<decay_t<result_of_t<F(size_t, typename T::value_type)>>> res(v.size());
  size_t i = 0;
  for (auto it = v.begin(); it != v.end(); ++it, ++i)
    res[i] = f(i, *it);
  return res;
}
template <class T, class F> auto Select(const T &v, F f) {
  vector<typename T::value_type> res;
  for (const auto &e : v)
    if (f(e))
      res.push_back(e);
  return res;
}
template <class T, class F> vector<size_t> TrueIndex(const T &v, F f) {
  vector<size_t> res;
  size_t i = 0;
  for (const auto &e : v) {
    if (f(e))
      res.push_back(i);
    ++i;
  }
  return res;
}

// ---------------------------------------------------------------- //

int main() {
  int n = in;
  VL a(n), b(n);
  rep(i, n) in(a[i], b[i]);

  LL ans = 0, sum_b = 0;
  rep(i, n) if (a[i] < b[i]) {
    ans += a[i];
    sum_b += b[i] - a[i];
  }
  dump(ans, sum_b);

  auto comp = [](PLL p1, PLL p2) {
    return p1.first - p1.second > p2.first - p2.second;
  };

  priority_queue<PLL, vector<PLL>, decltype(comp)> pq{comp};
  rep(i, n) if (a[i] >= b[i]) { pq.emplace(a[i], b[i]); }
  dump(pq);

  while (!pq.empty()) {
    auto t = pq.top();
    pq.pop();
    LL minus = min(sum_b, t.first);
    sum_b -= minus;
    t.first -= minus;
    ans += minus;
    if (t.first < t.second) {
      ans += t.first;
      sum_b += t.second - t.first;
      t.second -= t.first;
      t.first = 0;
    } else {
      pq.push(t);
    }
    dump(sum_b, pq);
  }

  out(ans);
}

Fixed submission:
#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#define _SILENCE_CXX17_RESULT_OF_DEPRECATION_WARNING
#include "bits/stdc++.h"
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define FOR(i, m, n) for (int i = (m); i < (n); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; --i)
#define rfor(i, m, n) for (int i = (m); i >= (n); --i)
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define range_it(a, l, r) (a).begin() + (l), (a).begin() + (r)

using namespace std;
using LL = long long;
using ld = long double;
using VB = vector<bool>;
using VVB = vector<VB>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<LL>;
using VVL = vector<VL>;
using VS = vector<string>;
using VD = vector<double>;
using PII = pair<int, int>;
using VP = vector<PII>;
using PLL = pair<LL, LL>;
using VPL = vector<PLL>;
template <class T> using Grid = vector<vector<T>>;
template <class T> using PQ = priority_queue<T>;
template <class T> using PQS = priority_queue<T, vector<T>, greater<T>>;
constexpr int inf = (int)1e9;
constexpr LL inf_ll = (LL)1e18, MOD = 1000000007;
constexpr ld PI = M_PI, EPS = 1e-12;

template <class T> inline void Sort(T &a) noexcept { sort(all(a)); }
template <class T> inline void RSort(T &a) noexcept { sort(rall(a)); }
template <class T> inline void Reverse(T &a) noexcept { reverse(all(a)); }
template <class T> inline void Unique(T &a) noexcept {
  a.erase(unique(all(a)), a.end());
}
template <class T> inline T Sorted(T a) noexcept {
  Sort(a);
  return a;
}
template <class T> inline T RSorted(T a) noexcept {
  RSort(a);
  return a;
}
template <class T> inline T Reversed(T a) noexcept {
  Reverse(a);
  return a;
}
template <class T> inline T Uniqued(T a) noexcept {
  Unique(a);
  return a;
}
template <class T> inline auto Max(const T &a) noexcept {
  return *max_element(all(a));
}
template <class T> inline auto Min(const T &a) noexcept {
  return *min_element(all(a));
}
template <class T> inline int MaxPos(const T &a) noexcept {
  return max_element(all(a)) - a.begin();
}
template <class T> inline int MinPos(const T &a) noexcept {
  return min_element(all(a)) - a.begin();
}
template <class T, class U> inline int Count(const T &a, const U &v) noexcept {
  return count(all(a), v);
}
template <class T, class U> inline int Find(const T &a, const U &v) noexcept {
  return find(all(a), v) - a.begin();
}
template <class T, class U> inline U Sum(const T &a, const U &v) noexcept {
  return accumulate(all(a), v);
}
template <class T, class U> inline int Lower(const T &a, const U &v) noexcept {
  return lower_bound(all(a), v) - a.begin();
}
template <class T, class U> inline int Upper(const T &a, const U &v) noexcept {
  return upper_bound(all(a), v) - a.begin();
}
template <class T, class P> inline void RemoveIf(T &a, P f) noexcept {
  a.erase(remove_if(all(a), f), a.end());
}
template <class T> inline T Age(T n, T m) noexcept { return (n + m - 1) / m; }
template <class T> inline T Age2(T n, T m) noexcept { return Age(n, m) * m; }
template <class T> inline T Tri(T n) noexcept {
  return (n & 1) ? (n + 1) / 2 * n : n / 2 * (n + 1);
}
template <class T = long long> inline T BIT(int b) noexcept {
  return T{1} << b;
}
template <class T> inline T Gcd(T n, T m) noexcept {
  return m ? Gcd(m, n % m) : n;
}
template <class T> inline T Lcm(T n, T m) noexcept { return n / Gcd(n, m) * m; }
template <class T> inline T Pow(T a, T n) noexcept {
  T r = 1;
  while (n > 0) {
    if (n & 1)
      r *= a;
    a *= a;
    n /= 2;
  }
  return r;
}
template <class T> inline T Powmod(T a, T n, T m = MOD) noexcept {
  T r = 1;
  while (n > 0) {
    if (n & 1)
      r = r * a % m, n--;
    else
      a = a * a % m, n /= 2;
  }
  return r;
}
template <class T> inline bool chmax(T &a, const T &b) noexcept {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, const T &b) noexcept {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool inRange(const T &v, const T &min, const T &max) noexcept {
  return min <= v && v <= max;
}
inline string operator*(string s, int n) noexcept {
  string ret;
  rep(i, n) ret += s;
  return ret;
}

// --- input --- //
#if defined(_WIN32) || defined(ONLINE_JUDGE)
#define getchar_unlocked _getchar_nolock
#define putchar_unlocked _putchar_nolock
#endif
inline int gc() noexcept { return getchar_unlocked(); }
template <class T> inline void InputF(T &v) noexcept { cin >> v; }
inline void InputF(char &v) noexcept {
  while (isspace(v = gc()))
    ;
}
inline void InputF(string &v) noexcept {
  char c;
  for (InputF(c); !isspace(c); c = gc())
    v += c;
}
inline void InputF(int &v) noexcept {
  bool neg = false;
  v = 0;
  char c;
  InputF(c);
  if (c == '-') {
    neg = true;
    c = gc();
  }
  for (; isdigit(c); c = gc())
    v = v * 10 + (c - '0');
  if (neg)
    v = -v;
}
inline void InputF(long long &v) noexcept {
  bool neg = false;
  v = 0;
  char c;
  InputF(c);
  if (c == '-') {
    neg = true;
    c = gc();
  }
  for (; isdigit(c); c = gc())
    v = v * 10 + (c - '0');
  if (neg)
    v = -v;
}
inline void InputF(double &v) noexcept {
  double dp = 1;
  bool neg = false, adp = false;
  v = 0;
  char c;
  InputF(c);
  if (c == '-') {
    neg = true;
    c = gc();
  }
  for (; isdigit(c) || c == '.'; c = gc()) {
    if (c == '.')
      adp = true;
    else if (adp)
      v += (c - '0') * (dp *= 0.1);
    else
      v = v * 10 + (c - '0');
  }
  if (neg)
    v = -v;
}
template <class T, class U> inline void InputF(pair<T, U> &v) noexcept {
  InputF(v.first);
  InputF(v.second);
}
template <class T> inline void InputF(vector<T> &v) noexcept {
  for (auto &e : v)
    InputF(e);
}
template <class T> inline T InputF() {
  T v;
  InputF(v);
  return v;
}
struct InputV {
  int n, m;
  InputV(int N) : n(N), m(0) {}
  InputV(pair<int, int> N) : n(N.first), m(N.second) {}
  template <class T> operator vector<T>() noexcept {
    vector<T> v(n);
    InputF(v);
    return v;
  }
  template <class T> operator vector<vector<T>>() noexcept {
    vector<vector<T>> v(n, vector<T>(m));
    InputF(v);
    return v;
  }
};
struct Input {
  template <class T> operator T() noexcept { return InputF<T>(); }
  int operator--(int) {
    int v;
    InputF(v);
    v--;
    return v;
  }
  InputV operator[](int n) noexcept { return InputV(n); }
  InputV operator[](pair<int, int> n) noexcept { return InputV(n); }
  void operator()() {}
  template <class H, class... T> void operator()(H &&h, T &&...t) {
    InputF(h);
    operator()(forward<T>(t)...);
  }
  template <class T, size_t W> array<vector<T>, W> get(int H) {
    array<vector<T>, W> ret;
    rep(i, H) rep(j, W) {
      T x = *this;
      ret[j].push_back(x);
    }
    return ret;
  }
} in;
#define input(type) InputF<type>()

// --- output --- //
struct BoolStr {
  const char *t, *f;
  BoolStr(const char *_t, const char *_f) : t(_t), f(_f) {}
} Yes("Yes", "No"), yes("yes", "no"), YES("YES", "NO"), Int("1", "0");
struct DivStr {
  const char *d, *l;
  DivStr(const char *_d, const char *_l) : d(_d), l(_l) {}
} spc(" ", "\n"), no_spc("", "\n"), end_line("\n", "\n"), comma(",", "\n"),
    no_endl(" ", "");
class Output {
  BoolStr B{Yes};
  DivStr D{spc};
  bool isPrint = true;
  void p(double v) { printf("%.20f", v); }
  void p(long double v) { printf("%.20Lf", v); }
  void p(int v) { printf("%d", v); }
  void p(LL v) { printf("%lld", v); }
  void p(char v) { putchar(v); }
  void p(bool v) { printf("%s", v ? B.t : B.f); }
  template <class T> void p(const T &v) { cout << v; }
  template <class T, class U> void p(const pair<T, U> &v) {
    p(v.first);
    printf("%s", D.d);
    p(v.second);
  }
  template <class T> void p(const vector<T> &v) {
    rep(i, sz(v)) {
      if (i)
        printf("%s", D.d);
      p(v[i]);
    }
  }
  template <class T> void p(const vector<vector<T>> &v) {
    rep(i, sz(v)) {
      if (i)
        printf("%s", D.l);
      p(v[i]);
    }
  }
  void p(const BoolStr &v) {
    B = v;
    isPrint = false;
  }
  void p(const DivStr &v) {
    D = v;
    isPrint = false;
  }

public:
  Output &operator()() {
    printf("%s", D.l);
    return *this;
  }
  template <class H> Output &operator()(H &&h) {
    p(h);
    if (isPrint)
      printf("%s", D.l);
    isPrint = true;
    return *this;
  }
  template <class H, class... T> Output &operator()(H &&h, T &&...t) {
    p(h);
    if (isPrint)
      printf("%s", D.d);
    isPrint = true;
    return operator()(forward<T>(t)...);
  }
  template <class... T> void exit(T &&...t) {
    operator()(forward<T>(t)...);
    std::exit(EXIT_SUCCESS);
  }
  Output &flush() {
    cout.flush();
    return *this;
  }
} out;

// --- dump --- //
#if __has_include("dump.hpp")
#include "dump.hpp"
#else
#define dump(...) (void(0))
#endif

template <class F> auto MakeVector(size_t size, F f) {
  vector<decay_t<result_of_t<F(size_t)>>> res(size);
  for (size_t i = 0; i < size; ++i)
    res[i] = f(i);
  return res;
}
template <class T> T Slice(const T &v, size_t i, size_t len) {
  return i < v.size()
             ? vector<T>(v.begin() + i, v.begin() + min(i + len, v.size()))
             : vector<T>();
}
template <class T, class F> void Each(T &v, F f) {
  for (auto &e : v)
    f(e);
}
template <class T, class F> auto Map(const T &v, F f) {
  vector<decay_t<result_of_t<F(typename T::value_type)>>> res(v.size());
  size_t i = 0;
  for (const auto &e : v)
    res[i++] = f(e);
  return res;
}
template <class T, class F> auto MapIndex(const T &v, F f) {
  vector<decay_t<result_of_t<F(size_t, typename T::value_type)>>> res(v.size());
  size_t i = 0;
  for (auto it = v.begin(); it != v.end(); ++it, ++i)
    res[i] = f(i, *it);
  return res;
}
template <class T, class F> auto Select(const T &v, F f) {
  vector<typename T::value_type> res;
  for (const auto &e : v)
    if (f(e))
      res.push_back(e);
  return res;
}
template <class T, class F> vector<size_t> TrueIndex(const T &v, F f) {
  vector<size_t> res;
  size_t i = 0;
  for (const auto &e : v) {
    if (f(e))
      res.push_back(i);
    ++i;
  }
  return res;
}

// ---------------------------------------------------------------- //

int main() {
  int n = in;
  VL a(n), b(n);
  rep(i, n) in(a[i], b[i]);
  if (a == b) {
    out.exit(0);
  }
  LL sum = Sum(a, 0LL);
  LL mi = inf_ll;
  rep(i, n) { a[i] > b[i] && chmin(mi, b[i]); }
  out(sum - mi);
}