#ifdef __LOCAL #include // プリコンパイル済みヘッダ ~/local/include/mytemplate.hpp.gch #else #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #endif using namespace std; // #include // using bint = boost::multiprecision::cpp_int; using int128 = __int128_t; using ll = long long; using vl = vector; using vvl = vector; using vb = vector; using vvb = vector; using vd = vector; using vvd = vector; using vc = vector; using vvc = vector; using pll = pair; #define REP1(i, n) REP3(i, 0, n, 1) #define REP2(i, s, n) REP3(i, s, n, 1) #define REP3(i, s, n, d) for(ll i = (ll)(s); i < (ll)(n); i += (d)) #define REP_OVERLOAD(e1, e2, e3, e4, NAME,...) NAME #define rep(...) REP_OVERLOAD(__VA_ARGS__, REP3, REP2, REP1)(__VA_ARGS__) #define DEP1(i, n) DEP3(i, n, -1, 1) #define DEP2(i, n, s) DEP3(i, n, s, 1) #define DEP3(i, n, s, d) for(ll i = (ll)(n); (ll)(s) < i; i -= (d)) #define DEP_OVERLOAD(e1, e2, e3, e4, NAME,...) NAME #define dep(...) DEP_OVERLOAD(__VA_ARGS__, DEP3, DEP2, DEP1)(__VA_ARGS__) #define fore(e, a) for (auto&& e: (a)) #define len(a) (ll)(a).size() #define all(a) (a).begin(), (a).end() #define rall(a) (a).rbegin(), (a).rend() #define pb push_back #define eb emplace_back #define fi first #define se second #define th third /********* C O N S T A N T **********/ constexpr ll INF = LONG_LONG_MAX / 2 - 10000LL; // 4,611,686,018,427,377,903 ~= 4.6e+18, 19桁 const double PI = acos(-1); /********* P A I R **********/ template inline pair& operator+=(pair& a, const pair& b) {a.fi += b.fi; a.se += b.se; return a;} template inline pair& operator-=(pair& a, const pair& b) {a.fi -= b.fi; a.se -= b.se; return a;} template inline pair& operator*=(pair& a, const pair& b) {a.fi *= b.fi; a.se *= b.se; return a;} template inline pair& operator/=(pair& a, const pair& b) {a.fi /= b.fi; a.se /= b.se; return a;} template inline pair& operator%=(pair& a, const pair& b) {a.fi %= b.fi; a.se %= b.se; return a;} template inline pair& operator+=(pair& a, const V& b) {a.fi += b; a.se += b; return a;} template inline pair& operator-=(pair& a, const V& b) {a.fi -= b; a.se -= b; return a;} template inline pair& operator*=(pair& a, const V& b) {a.fi *= b; a.se *= b; return a;} template inline pair& operator/=(pair& a, const V& b) {a.fi /= b; a.se /= b; return a;} template inline pair& operator%=(pair& a, const V& b) {a.fi %= b; a.se %= b; return a;} template inline pair operator+(pair a, const V& b) {a += b; return a;} template inline pair operator-(pair a, const V& b) {a -= b; return a;} template inline pair operator*(pair a, const V& b) {a *= b; return a;} template inline pair operator/(pair a, const V& b) {a /= b; return a;} template inline pair operator%(pair a, const V& b) {a %= b; return a;} template inline pair operator+(pair a) {return a;} template inline pair operator-(pair a) {return a * (-1);} template istream& operator >>(istream& stream, pair& a) {stream >> a.fi >> a.se; return stream;} template ostream& operator <<(ostream &stream, const pair& a) { stream << a.fi << " " << a.se; return stream; } /********* V E C T O R **********/ template inline vector& operator+=(vector& a, const vector& b) {assert(a.size() == b.size()); rep(i, 0, a.size()) a[i] += b[i]; return a;} template inline vector& operator-=(vector& a, const vector& b) {assert(a.size() == b.size()); rep(i, 0, a.size()) a[i] -= b[i]; return a;} template inline vector& operator*=(vector& a, const vector& b) {assert(a.size() == b.size()); rep(i, 0, a.size()) a[i] *= b[i]; return a;} template inline vector& operator/=(vector& a, const vector& b) {assert(a.size() == b.size()); rep(i, 0, a.size()) a[i] /= b[i]; return a;} template inline vector& operator%=(vector& a, const vector& b) {assert(a.size() == b.size()); rep(i, 0, a.size()) a[i] %= b[i]; return a;} template inline vector& operator+=(vector& a, const U& b) {fore(e, a) e += b; return a;} template inline vector& operator-=(vector& a, const U& b) {fore(e, a) e -= b; return a;} template inline vector& operator*=(vector& a, const U& b) {fore(e, a) e *= b; return a;} template inline vector& operator/=(vector& a, const U& b) {fore(e, a) e /= b; return a;} template inline vector& operator%=(vector& a, const U& b) {fore(e, a) e %= b; return a;} template inline vector operator+(vector a, const U& b) {a += b; return a;} template inline vector operator-(vector a, const U& b) {a -= b; return a;} template inline vector operator*(vector a, const U& b) {a *= b; return a;} template inline vector operator/(vector a, const U& b) {a /= b; return a;} template inline vector operator%(vector a, const U& b) {a %= b; return a;} template inline vector operator+(vector a) {return a;} template inline vector operator-(vector a) {return a * (-1);} template istream& operator >>(istream& stream, vector& a) {fore(e, a) stream >> e; return stream;} template ostream& operator <<(ostream& stream, const vector& v) {if(v.size()){stream << v[0]; rep(i, 1, v.size()) cout << " " << v[i];} return stream;} template ostream& operator <<(ostream& stream, const vector>& vv) {if(vv.size()){stream << vv[0]; rep(i, 1, vv.size()) cout << '\n' << vv[i];} return stream;} template inline T Sum(const vector& v) {return reduce(all(v));} // v.size() == 0 のとき T() を返す template inline T Max(const vector& v) {assert(v.size()); return *max_element(all(v));} template inline T Min(const vector& v) {assert(v.size()); return *min_element(all(v));} template inline ll Argmax(const vector& v) {assert(v.size()); return max_element(all(v)) - v.begin();} template inline ll Argmin(const vector& v) {assert(v.size()); return min_element(all(v)) - v.begin();} template inline bool Contains(const vector& v, const U& a) {return find(all(v), a) != v.end();} template vector make_vector(int n, U v) { return vector(n, v); } template auto make_vector(int n, Args... args) {auto val = make_vector(args...); return make_vector(n, move(val));} /********* S E T **********/ template istream& operator >>(istream& stream, set& st) {T e; stream >> e; st.insert(e); return stream;} template ostream& operator <<(ostream& stream, const set& st) {if(st.size()){auto it=st.begin(); stream << *it++; for(; it!=st.end(); it++) cout << " " << *it;} return stream;} template inline T Max(const set& st) {assert(st.size()); return *prev(st.end());} template inline T Min(const set& st) {assert(st.size()); return *st.begin();} template inline bool Contains(const set& st, T x) {return st.find(x) != st.end();} /********* M U L T I S E T **********/ template istream& operator >>(istream& stream, multiset& st) {T e; stream >> e; st.insert(e); return stream;} template ostream& operator <<(ostream& stream, const multiset& st) {if(st.size()){auto it=st.begin(); stream << *it++; for(; it!=st.end(); it++) cout << " " << *it;} return stream;} template inline T Max(const multiset& st) {assert(st.size()); return *prev(st.end());} template inline T Min(const multiset& st) {assert(st.size()); return *st.begin();} template inline bool Contains(const multiset& st, T x) {return st.find(x) != st.end();} template inline bool EraseOne(multiset& st, T x) {auto it=st.find(x); if (it!=st.end()) {st.erase(it); return true;} else return false;} // 要素xを1つ削除. 消せたらtrueを返す. /********* S T R I N G **********/ template inline bool Contains(const string& s, const T& c) {return s.find(c) != string::npos;} // cはchar, string共に可 inline string ToUpper(const string& s) {string t; t.resize(s.size()); std::transform(all(s), t.begin(), ::toupper); return t; } inline string ToLower(const string& s) {string t; t.resize(s.size()); std::transform(all(s), t.begin(), ::tolower); return t; } /********* T R I O **********/ template struct trio { T1 first; T2 second; T3 third; // コンストラクタ・代入演算子 trio() {first=T1(); second=T2(); third=T3();} trio(const T1& x) : first(x), second(x), third(x) {} trio(const T1& x, const T2& y, const T3& z) : first(x), second(y), third(z) {} trio(const trio& t) {first=t.first; second=t.second; third=t.third;} // コピーコンストラクタ trio& operator =(const trio& t) {first=t.first; second=t.second; third=t.third; return *this;} // 比較演算子 bool operator <(const trio& t) const {return tie(first, second, third) < tie(t.first, t.second, t.third);} bool operator ==(const trio& t) const {return tie(first, second, third) == tie(t.first, t.second, t.third);} bool operator !=(const trio& other) const { return !(*this == other); } bool operator >(const trio& other) const { return other < *this; } bool operator <=(const trio& other) const { return !(*this > other); } bool operator >=(const trio& other) const { return !(*this < other); } // 単項演算子（+ -） trio operator +() const { return *this; } trio operator -() const { return (-1) * (*this); } // 複合代入演算子 trio& operator +=(const trio& t) {first += t.first; second += t.second; third += t.third; return *this;} trio& operator -=(const trio& t) {first -= t.first; second -= t.second; third -= t.third; return *this;} trio& operator *=(const trio& t) {first *= t.first; second *= t.second; third *= t.third; return *this;} trio& operator /=(const trio& t) {first /= t.first; second /= t.second; third /= t.third; return *this;} trio& operator %=(const trio& t) {first %= t.first; second %= t.second; third %= t.third; return *this;} // 算術演算子 friend trio operator +(const trio& lhs, const trio& rhs) {return trio(lhs) += rhs;} friend trio operator -(const trio& lhs, const trio& rhs) {return trio(lhs) -= rhs;} friend trio operator *(const trio& lhs, const trio& rhs) {return trio(lhs) *= rhs;} friend trio operator /(const trio& lhs, const trio& rhs) {return trio(lhs) /= rhs;} friend trio operator %(const trio& lhs, const trio& rhs) {return trio(lhs) %= rhs;} // 入出力 friend istream& operator >>(istream &stream, trio& t) {return stream >> t.first >> t.second >> t.third;} friend ostream& operator <<(ostream &stream, const trio& t) {return stream << t.first << " " << t.second << " " << t.third;} operator tuple() {return tie(first, second, third);} }; using tll = trio; /********* R A N D O M **********/ struct Random { mt19937_64 rnd; Random() { random_device seed_gen; rnd.seed(seed_gen()); } ll randint(ll a, ll b) { // [a, b] uniform_int_distribution dist(a, b); return dist(rnd); } double randreal(double a, double b) { uniform_real_distribution dist(a, b); return dist(rnd); } char randchar(char a, char b) { // [a, b] uniform_int_distribution dist(a, b); return dist(rnd); } }; /********* P R I N T **********/ template inline void print(const T& e) {cout << e << '\n';} template inline void print(const H& h, const T&... t) {cout << h << ' '; print(t...);} template inline void End(const T&... t) {print(t...); exit(0);} /********* D E B U G **********/ #ifdef __LOCAL #define debug(...) if(DEBUG) do{cout << '[' << #__VA_ARGS__ << "] ";debug_(__VA_ARGS__);}while(0) #else #define debug(...) #endif void dbg_(const long long& e) {if (e == INF) cout << "INF"; else if (e == -INF) cout << "-INF"; else cout << e;} template void dbg_(const T& e) {cout << e;} template void dbg_(const pair& p) {cout << '('; dbg_(p.first); cout << ' '; dbg_(p.second); cout << ')';} template void dbg_(const trio& t) {cout << '('; dbg_(t.first); cout << ' '; dbg_(t.second); cout << ' '; dbg_(t.third); cout << ')';} template void debug_(const T& e) {dbg_(e); cout << '\n';} template void debug_(const vector& v) {if (v.size()){auto it=v.begin(); dbg_(*it++); for(; it!=v.end(); ++it){cout << ' '; dbg_(*it);}} cout << '\n';} template void debug_(const vector>& vv) {cout << '\n'; ll cnt=0; for(auto&& v : vv){cout << cnt++ << ": "; debug_(v);}} template void debug_(const map& mp) {if (mp.size()) {auto it = mp.begin(); dbg_(*it++); for(; it != mp.end(); ++it) {cout << ' '; dbg_(*it);}} cout << '\n';} template void debug_(const vector>& vm){cout << '\n'; ll cnt=0; for(auto&& mp : vm){cout << cnt++ << ": "; debug_(mp);}} template void debug_(const set& st) {if(st.size()){auto it=st.begin(); dbg_(*it++); for(; it!=st.end(); ++it) {cout << ' '; dbg_(*it);}}cout << '\n';} template void debug_(const multiset& st) {if(st.size()) {auto it=st.begin(); dbg_(*it++); for(; it != st.end(); ++it) {cout << ' '; dbg_(*it);}} cout << '\n';} template void debug_(const vector>& vs) {cout << '\n'; ll cnt=0; for(auto&& st : vs){cout << cnt++ << ": "; debug_(st);}} template void debug_(const vector>& vs) {cout << '\n'; ll cnt=0;for(auto&& st : vs){cout << cnt++ << ": "; debug_(st);}} template void debug_(const H& h, const T&... t) {dbg_(h); cout << ", "; debug_(t...);} /********* O T H E R S **********/ template inline bool chmin(T& a, U b) {if (a > b) {a = b; return true;} return false;} // bは値渡し! template inline bool chmax(T& a, U b) {if (a < b) {a = b; return true;} return false;} template inline auto Mod(const T& a, const U& m) {return (a % m + m) % m;} // 負もOK template inline auto Ceil(const T& x, const U& y) {return x < 0 ? x/y : (x + y - 1) / y;} // 負もOK template inline auto Floor(const T& x, const U& y) {return -(Ceil(-x, y)); } // 負もOK inline ll Isqrt(ll n) {assert(n >= 0); ll x = round(sqrt(n)); while(x * x > n) --x; return x;} inline ll Comb(ll n, ll r) {if (r < 0 || n < r) return 0; r = min(r, n - r); ll ret = 1; rep(i, r) {ret *= n - i; ret /= i + 1;} return ret;} // n=60, r=30までOK template inline T Pow(T x, ll n) {assert(n >= 0); T ret = 1; while(1) {if (n % 2) ret *= x; n /= 2; if(!n) return ret; x = x * x;}} // べき乗 mintもOK template inline T Aseries(T a, T d, ll n) {assert(n >= 0); return a * n + n * (n - 1) / 2 * d;} // 等差級数 mintもOK template inline T Gseries(T a, T r, ll n) {assert(n >= 0); if (r == 1) return a * n; else return a * (1 - Pow(r, n)) / (1 - r);} // 等比級数 mintもOK template using min_priority_queue = priority_queue, greater>; inline bool Bit(ll b, int i) {assert(0 <= i && i < 64); return (b >> i) & 1;} inline ll Popcount(ll b) {return __builtin_popcountll(b);} inline ll Mask(ll n) {assert(0 <= n && n < 63); return (1LL << n) - 1LL;} // [0, n)のbitが立った64bit整数を返す。 inline ll Mask(ll n, ll m) {assert(n >= m); return Mask(n) ^ Mask(m);} // [m, n)のbitが立った64bit整数を返す。 /********* M O D **********/ // #include // https://atcoder.github.io/ac-library/production/document_ja/ // using namespace atcoder; // using mint = modint998244353; // modint1000000007; // istream& operator >>(istream& stream, mint& e) {ll n; stream >> n; e = n; return stream; } // ostream& operator <<(ostream& stream, const mint& e) { stream << e.val(); return stream; } // using vm = vector; // using vvm = vector; /***************************************/ constexpr bool DEBUG = true; int main() { cin.tie(nullptr); cout << fixed << setprecision(10); ll N; cin >> N; vector P(N); cin >> P; map mp; rep(i, N) { auto p = P[i]; mp[p] = i + 1; } sort(all(P)); vector ans; rep(i, 0, N, 2) { if (i == N - 1) break; auto p1 = P[i]; auto p2 = P[i + 1]; ans.eb(mp[p1], mp[p2]); } print(len(ans)); fore(e, ans) print(e); }