Problem p03721 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define srep(i, s, t) for (int i = s; i < t; ++i)
#define rng(a) a.begin(), a.end()
#define rrng(a) a.rbegin(), a.rend()
#define maxs(x, y) (x = max(x, y))
#define mins(x, y) (x = min(x, y))
#define limit(x, l, r) max(l, min(x, r))
#define lims(x, l, r) (x = max(l, min(x, r)))
#define isin(x, l, r) ((l) <= (x) && (x) < (r))
#define pb push_back
#define eb emplace_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define uni(x) x.erase(unique(rng(x)), x.end())
#define snuke srand((unsigned)clock() + (unsigned)time(NULL));
#define show(x) cout << #x << " = " << x << endl;
#define PQ(T) priority_queue<T, v(T), greater<T>>
#define bn(x) ((1 << x) - 1)
#define dup(x, y) (((x) + (y)-1) / (y))
#define newline puts("")
#define v(T) vector<T>
#define vv(T) v(v(T))
typedef long long int ll;
typedef unsigned uint;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef tuple<int, int, int> T;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
typedef vector<T> vt;
inline int getInt() {
  int x;
  scanf("%d", &x);
  return x;
}
template <typename T> inline istream &operator>>(istream &i, v(T) & v) {
  rep(j, sz(v)) i >> v[j];
  return i;
}
template <typename T> string join(const v(T) & v) {
  stringstream s;
  rep(i, sz(v)) s << ' ' << v[i];
  return s.str().substr(1);
}
template <typename T> inline ostream &operator<<(ostream &o, const v(T) & v) {
  if (sz(v))
    o << join(v);
  return o;
}
template <typename T1, typename T2>
inline istream &operator>>(istream &i, pair<T1, T2> &v) {
  return i >> v.fi >> v.se;
}
template <typename T1, typename T2>
inline ostream &operator<<(ostream &o, const pair<T1, T2> &v) {
  return o << v.fi << "," << v.se;
}
template <typename T> inline ll suma(const v(T) & a) {
  ll res(0);
  for (auto &&x : a)
    res += x;
  return res;
}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
const int MX = 200005;
#define dame                                                                   \
  {                                                                            \
    puts("-1");                                                                \
    return 0;                                                                  \
  }
#define yn                                                                     \
  { puts("Yes"); }                                                             \
  else {                                                                       \
    puts("No");                                                                \
  }
//---------------------------------------------------------------
#define fastio std::ios::sync_with_stdio(false);
#define myio                                                                   \
  ifstream iofi;                                                               \
  if (argc > 1) {                                                              \
    iofi.open(argv[1]);                                                        \
    std::cin.rdbuf(iofi.rdbuf());                                              \
  }
using u32 = int32_t;
using u64 = int64_t;
//--------------------------------------------------------------

int main(int argc, char **argv) {
  fastio;
  myio;
  int n, k;
  cin >> n >> k;
  priority_queue<P, vp, greater<P>> q;
  rep(i, n) {
    P a;
    cin >> a;
    q.push(a);
  }
  int ans;
  ll sum = 0;
  while (sum < k) {
    ans = q.top().fi;
    sum += q.top().se;
    q.pop();
  }
  // cout<<sum<<endl;
  cout << ans << endl;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define srep(i, s, t) for (int i = s; i < t; ++i)
#define rng(a) a.begin(), a.end()
#define rrng(a) a.rbegin(), a.rend()
#define maxs(x, y) (x = max(x, y))
#define mins(x, y) (x = min(x, y))
#define limit(x, l, r) max(l, min(x, r))
#define lims(x, l, r) (x = max(l, min(x, r)))
#define isin(x, l, r) ((l) <= (x) && (x) < (r))
#define pb push_back
#define eb emplace_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define uni(x) x.erase(unique(rng(x)), x.end())
#define snuke srand((unsigned)clock() + (unsigned)time(NULL));
#define show(x) cout << #x << " = " << x << endl;
#define PQ(T) priority_queue<T, v(T), greater<T>>
#define bn(x) ((1 << x) - 1)
#define dup(x, y) (((x) + (y)-1) / (y))
#define newline puts("")
#define v(T) vector<T>
#define vv(T) v(v(T))
typedef long long int ll;
typedef unsigned uint;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef tuple<int, int, int> T;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
typedef vector<T> vt;
inline int getInt() {
  int x;
  scanf("%d", &x);
  return x;
}
template <typename T> inline istream &operator>>(istream &i, v(T) & v) {
  rep(j, sz(v)) i >> v[j];
  return i;
}
template <typename T> string join(const v(T) & v) {
  stringstream s;
  rep(i, sz(v)) s << ' ' << v[i];
  return s.str().substr(1);
}
template <typename T> inline ostream &operator<<(ostream &o, const v(T) & v) {
  if (sz(v))
    o << join(v);
  return o;
}
template <typename T1, typename T2>
inline istream &operator>>(istream &i, pair<T1, T2> &v) {
  return i >> v.fi >> v.se;
}
template <typename T1, typename T2>
inline ostream &operator<<(ostream &o, const pair<T1, T2> &v) {
  return o << v.fi << "," << v.se;
}
template <typename T> inline ll suma(const v(T) & a) {
  ll res(0);
  for (auto &&x : a)
    res += x;
  return res;
}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
const int MX = 200005;
#define dame                                                                   \
  {                                                                            \
    puts("-1");                                                                \
    return 0;                                                                  \
  }
#define yn                                                                     \
  { puts("Yes"); }                                                             \
  else {                                                                       \
    puts("No");                                                                \
  }
//---------------------------------------------------------------
#define fastio std::ios::sync_with_stdio(false);
#define myio                                                                   \
  ifstream iofi;                                                               \
  if (argc > 1) {                                                              \
    iofi.open(argv[1]);                                                        \
    std::cin.rdbuf(iofi.rdbuf());                                              \
  }
using u32 = int32_t;
using u64 = int64_t;
//--------------------------------------------------------------

int main(int argc, char **argv) {
  fastio;
  myio;
  int n;
  ll k;
  cin >> n >> k;
  priority_queue<P, vp, greater<P>> q;
  rep(i, n) {
    P a;
    cin >> a;
    q.push(a);
  }
  int ans;
  ll sum = 0;
  while (sum < k) {
    ans = q.top().fi;
    sum += q.top().se;
    q.pop();
  }
  // cout<<sum<<endl;
  cout << ans << endl;
}