#include using namespace std; #define REP(i,n) for(ll i=0;i<(ll)n;i++) #define dump(x) cerr << "Line " << __LINE__ << ": " << #x << " = " << (x) << "\n"; #define spa << " " << #define fi first #define se second #define ALL(a) (a).begin(),(a).end() #define ALLR(a) (a).rbegin(),(a).rend() using ld = long double; using ll = long long; using ull = unsigned long long; using pii = pair; using pll = pair; using pdd = pair; template using V = vector; template using P = pair; template vector make_vec(size_t n, T a) { return vector(n, a); } template auto make_vec(size_t n, Ts... ts) { return vector(n, make_vec(ts...)); } template ostream& operator << (ostream& os, const pair v){os << "(" << v.first << ", " << v.second << ")"; return os;} template ostream& operator<<(ostream &os, const vector &v) { for (auto &e : v) os << e << ' '; return os; } template ostream& operator<<(ostream& os, const vector> &v){ for(auto &e : v){os << e << "\n";} return os;} struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_; template void UNIQUE(vector &x) {sort(ALL(x));x.erase(unique(ALL(x)), x.end());} template bool chmax(T &a, const T &b) { if (a bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; } void fail() { cout << -1 << '\n'; exit(0); } inline int popcount(const int x) { return __builtin_popcount(x); } inline int popcount(const ll x) { return __builtin_popcountll(x); } template void debug(vector>&v,ll h,ll w){for(ll i=0;i void debug(vector&v,ll n){if(n!=0)cerr< struct edge { int src, to; T cost; edge(int to, T cost) : src(-1), to(to), cost(cost) {} edge(int src, int to, T cost) : src(src), to(to), cost(cost) {} edge &operator=(const int &x) { to = x; return *this; } operator int() const { return to; } }; template< typename T > using Edges = vector< edge< T > >; template< typename T > using WeightedGraph = vector< Edges< T > >; using UnWeightedGraph = vector< vector< int > >; template< typename T > using Matrix = vector< vector< T > >; template< typename T > vector< T > Dijkstra(WeightedGraph< T > &g, int s) { const auto INF = numeric_limits< T >::max(); vector< T > dist(g.size(), INF); using Pi = pair< T, int >; priority_queue< Pi, vector< Pi >, greater< Pi > > que; dist[s] = 0; que.emplace(dist[s], s); while(!que.empty()) { T cost; int idx; tie(cost, idx) = que.top(); que.pop(); if(dist[idx] < cost) continue; for(auto &e : g[idx]) { auto next_cost = cost + e.cost; if(dist[e.to] <= next_cost) continue; dist[e.to] = next_cost; que.emplace(dist[e.to], e.to); } } return dist; } int main(){ ll N, M, A, B; cin >> N >> M >> A >> B; A--, B--; V L(M), R(M); REP(i, M) cin >> L[i] >> R[i]; REP(i, M) L[i]--, R[i]--; using Graph = V>>; Graph G(N+1); REP(i, M){ G[L[i]].emplace_back(R[i]+1, 1); G[R[i]+1].emplace_back(L[i], 1); } REP(i, N+1){ if(i= INF ? -1 : res) << endl; return 0; }