Problem p02623 (C++)

Buggy submission (status: Time Limit Exceeded):
#define _GLIBCXX_DEBUG
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
#define rep0(TMS) for (int CNT = 0; CNT < (int)(TMS); CNT++)
#define rep(CNT, GOAL) for (int CNT = 0; CNT < (int)(GOAL); CNT++)
#define rep2(CNT, START, GOAL)                                                 \
  for (int CNT = (int)(START); CNT < (int)(GOAL); CNT++)
#define rep3(CNT, START, GOAL)                                                 \
  for (int CNT = (int)(START); CNT > (int)(GOAL); CNT--)
#define all(CONT) begin(CONT), end(CONT)
#define itrep(ITR, CONT) for (auto ITR = begin(CONT); ITR != end(CONT); ITR++)
#define itrep1(ITR, CONT)                                                      \
  for (auto ITR = next(begin(CONT)); ITR != end(CONT); ITR++)
template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
void prec(const int &DIG) {
  cerr << fixed << setprecision(DIG);
  cout << fixed << setprecision(DIG);
}
template <typename T> void CERR(const T &ELEM) { cerr << ELEM; }
template <typename T, typename... Ts>
void CERR(const T &FIRST, const Ts &...REST) {
  CERR(FIRST);
  cerr << ", ";
  CERR(REST...);
}
template <typename T1, typename T2> void CERR(const pair<T1, T2> &PAIR) {
  cerr << "(";
  CERR(PAIR.first);
  cerr << ", ";
  CERR(PAIR.second);
  cerr << ")";
}
template <typename T> void CERR(const vector<T> &VEC) {
  cerr << "{ ";
  itrep(ITR, VEC) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR1(const vector<T> &VEC) {
  cerr << "{ ";
  itrep1(ITR, VEC) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR(const set<T> &SET) {
  cerr << "{ ";
  itrep(ITR, SET) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR(const multiset<T> &MULTISET) {
  cerr << "{ ";
  itrep(ITR, MULTISET) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T1, typename T2> void CERR(const map<T1, T2> &MAP) {
  cerr << "{ ";
  itrep(ITR, MAP) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
#define db(OBJ)                                                                \
  cerr << #OBJ << ": ";                                                        \
  CERR(OBJ);                                                                   \
  cerr << ", "
#define dbl(OBJ)                                                               \
  cerr << #OBJ << ": ";                                                        \
  CERR(OBJ);                                                                   \
  cerr << "\n"
#define db1(OBJ)                                                               \
  cerr << #OBJ << ": ";                                                        \
  CERR1(OBJ);                                                                  \
  cerr << "\n"
#define dbs(...)                                                               \
  cerr << "(" << #__VA_ARGS__ << "): (";                                       \
  CERR(__VA_ARGS__);                                                           \
  cerr << ")\n"
#define dbvv(VV)                                                               \
  cerr << #VV << ": {\n";                                                      \
  rep(CNT, VV.size()) {                                                        \
    cerr << #VV << "[" << CNT << "]: ";                                        \
    CERR(VV[CNT]);                                                             \
    cerr << ",\n";                                                             \
  }                                                                            \
  cerr << "}\n"
#define db01(VV)                                                               \
  cerr << #VV << ": {\n";                                                      \
  rep(CNT, VV.size()) {                                                        \
    cerr << #VV << "[" << CNT << "]: ";                                        \
    CERR1(VV[CNT]);                                                            \
    cerr << ",\n";                                                             \
  }                                                                            \
  cerr << "}\n"
#define db10(VV)                                                               \
  cerr << #VV << ": {\n";                                                      \
  rep2(CNT, 1, VV.size()) {                                                    \
    cerr << #VV << "[" << CNT << "]: ";                                        \
    CERR(VV[CNT]);                                                             \
    cerr << ",\n";                                                             \
  }                                                                            \
  cerr << "}\n"
#define db11(VV)                                                               \
  cerr << #VV << ": {\n";                                                      \
  rep2(CNT, 1, VV.size()) {                                                    \
    cerr << #VV << "[" << CNT << "]: ";                                        \
    CERR1(VV[CNT]);                                                            \
    cerr << ",\n";                                                             \
  }                                                                            \
  cerr << "}\n"
#define YN(FLG) cout << (FLG ? "YES" : "NO") << "\n"
#define Yn(FLG) cout << (FLG ? "Yes" : "No") << "\n"
#define yn(FLG) cout << (FLG ? "yes" : "no") << "\n"
// const ll INF = 1'000'000'000'000'000'007;
const int INF = 1'000'000'007;
const ll MOD = 1'000'000'007; // 998'244'353;

int main() {
  ll N, M, K;
  cin >> N >> M >> K;
  // dbs(N, M, K);
  vector<ll> A(N);
  rep(i, N) cin >> A[i];
  vector<ll> B(M);
  rep(i, M) cin >> B[i];
  // dbl(A); dbl(B);
  // Aの[0,i)の累積和，Bの[0,i)の累積和
  vector<ll> accA(N + 1), accB(M + 1);
  rep(i, N) accA[i + 1] = accA[i] + A[i];
  rep(i, M) accB[i + 1] = accB[i] + B[i];
  // dbl(A); dbl(accA); dbl(B); dbl(accB);
  // 机Aの[0,i)(i冊)を読んだとき，Bを何冊[0,j)(j冊)読めるかを考える
  int ans = 0;
  rep(i, N + 1) {
    if (K - accA[i] < 0)
      break;
    int j = upper_bound(all(accB), K - accA[i]) - begin(accB) - 1;
    // dbl(i); dbs(accA[i], K - accA[i]); dbl(j); dbl(i + j);
    chmax(ans, i + j);
  }

  cout << ans << endl;
}

Fixed submission:
// #define _GLIBCXX_DEBUG
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;
#define rep0(TMS) for (int CNT = 0; CNT < (int)(TMS); CNT++)
#define rep(CNT, GOAL) for (int CNT = 0; CNT < (int)(GOAL); CNT++)
#define rep2(CNT, START, GOAL)                                                 \
  for (int CNT = (int)(START); CNT < (int)(GOAL); CNT++)
#define rep3(CNT, START, GOAL)                                                 \
  for (int CNT = (int)(START); CNT > (int)(GOAL); CNT--)
#define all(CONT) begin(CONT), end(CONT)
#define itrep(ITR, CONT) for (auto ITR = begin(CONT); ITR != end(CONT); ITR++)
#define itrep1(ITR, CONT)                                                      \
  for (auto ITR = next(begin(CONT)); ITR != end(CONT); ITR++)
template <typename T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
void prec(const int &DIG) {
  cerr << fixed << setprecision(DIG);
  cout << fixed << setprecision(DIG);
}
template <typename T> void CERR(const T &ELEM) { cerr << ELEM; }
template <typename T, typename... Ts>
void CERR(const T &FIRST, const Ts &...REST) {
  CERR(FIRST);
  cerr << ", ";
  CERR(REST...);
}
template <typename T1, typename T2> void CERR(const pair<T1, T2> &PAIR) {
  cerr << "(";
  CERR(PAIR.first);
  cerr << ", ";
  CERR(PAIR.second);
  cerr << ")";
}
template <typename T> void CERR(const vector<T> &VEC) {
  cerr << "{ ";
  itrep(ITR, VEC) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR1(const vector<T> &VEC) {
  cerr << "{ ";
  itrep1(ITR, VEC) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR(const set<T> &SET) {
  cerr << "{ ";
  itrep(ITR, SET) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T> void CERR(const multiset<T> &MULTISET) {
  cerr << "{ ";
  itrep(ITR, MULTISET) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
template <typename T1, typename T2> void CERR(const map<T1, T2> &MAP) {
  cerr << "{ ";
  itrep(ITR, MAP) {
    CERR(*ITR);
    cerr << ", ";
  }
  cerr << "}";
}
#define db(OBJ)                                                                \
  cerr << #OBJ << ": ";                                                        \
  CERR(OBJ);                                                                   \
  cerr << ", "
#define dbl(OBJ)                                                               \
  cerr << #OBJ << ": ";                                                        \
  CERR(OBJ);                                                                   \
  cerr << "\n"
#define db1(OBJ)                                                               \
  cerr << #OBJ << ": ";                                                        \
  CERR1(OBJ);                                                                  \
  cerr << "\n"
#define dbs(...)                                                               \
  cerr << "(" << #__VA_ARGS__ << "): (";                                       \
  CERR(__VA_ARGS__);                                                           \
  cerr << ")\n"
#define dbvv(VV)                                                               \
  cerr << #VV << ": {\n";                                                      \
  rep(CNT, VV.size()) {                                                        \
    cerr << #VV << "[" << CNT << "]: ";                                        \
    CERR(VV[CNT]);                                                             \
    cerr << ",\n";                                                             \
  }                                                                            \
  cerr << "}\n"
#define db01(VV)                                                               \
  cerr << #VV << ": {\n";                                                      \
  rep(CNT, VV.size()) {                                                        \
    cerr << #VV << "[" << CNT << "]: ";                                        \
    CERR1(VV[CNT]);                                                            \
    cerr << ",\n";                                                             \
  }                                                                            \
  cerr << "}\n"
#define db10(VV)                                                               \
  cerr << #VV << ": {\n";                                                      \
  rep2(CNT, 1, VV.size()) {                                                    \
    cerr << #VV << "[" << CNT << "]: ";                                        \
    CERR(VV[CNT]);                                                             \
    cerr << ",\n";                                                             \
  }                                                                            \
  cerr << "}\n"
#define db11(VV)                                                               \
  cerr << #VV << ": {\n";                                                      \
  rep2(CNT, 1, VV.size()) {                                                    \
    cerr << #VV << "[" << CNT << "]: ";                                        \
    CERR1(VV[CNT]);                                                            \
    cerr << ",\n";                                                             \
  }                                                                            \
  cerr << "}\n"
#define YN(FLG) cout << (FLG ? "YES" : "NO") << "\n"
#define Yn(FLG) cout << (FLG ? "Yes" : "No") << "\n"
#define yn(FLG) cout << (FLG ? "yes" : "no") << "\n"
// const ll INF = 1'000'000'000'000'000'007;
const int INF = 1'000'000'007;
const ll MOD = 1'000'000'007; // 998'244'353;

int main() {
  ll N, M, K;
  cin >> N >> M >> K;
  // dbs(N, M, K);
  vector<ll> A(N);
  rep(i, N) cin >> A[i];
  vector<ll> B(M);
  rep(i, M) cin >> B[i];
  // dbl(A); dbl(B);
  // Aの[0,i)の累積和，Bの[0,i)の累積和
  vector<ll> accA(N + 1), accB(M + 1);
  rep(i, N) accA[i + 1] = accA[i] + A[i];
  rep(i, M) accB[i + 1] = accB[i] + B[i];
  // dbl(A); dbl(accA); dbl(B); dbl(accB);
  // 机Aの[0,i)(i冊)を読んだとき，Bを何冊[0,j)(j冊)読めるかを考える
  int ans = 0;
  rep(i, N + 1) {
    if (K - accA[i] < 0)
      break;
    int j = upper_bound(all(accB), K - accA[i]) - begin(accB) - 1;
    // dbl(i); dbs(accA[i], K - accA[i]); dbl(j); dbl(i + j);
    chmax(ans, i + j);
  }

  cout << ans << endl;
}