func_code_string: #include <bits/stdc++.h>   using namespace std;   const int INF = 1e9 + 10;   const int maxn = 5e5 + 10;   int N, M;   struct edge {     int v, u, l, r;     edge() {}     edge(int v_, int u_, int l_, int r_) : v(v_), u(u_), l(l_), r(r_) {}     bool operator>(const edge& rhs) const { return l > rhs.l; }   };   priority_queue<edge, vector<edge>, greater<edge>> q;   vector<edge> adj[maxn][2];   int last[maxn][2];   void relax(int v, int start, int end) {     last[v][start & 1] = max(last[v][start & 1], end);     for (auto& e : adj[v][start & 1]) {       edge t = e;       t.l = start;       q.push(t);     }     adj[v][start & 1].clear();   }   int main() {     scanf( %d %d , &N, &M);     for (int i = 1; i <= M; ++i) {       int v, u, l, r;       scanf( %d %d %d %d , &v, &u, &l, &r);       --r;       q.push(edge(v, u, l, ((l & 1) == (r & 1) ? r : r - 1)));       q.push(edge(u, v, l, ((l & 1) == (r & 1) ? r : r - 1)));       q.push(edge(v, u, l + 1, (((l + 1) & 1) == (r & 1) ? r : r - 1)));       q.push(edge(u, v, l + 1, (((l + 1) & 1) == (r & 1) ? r : r - 1)));     }     if (N == 1) {       printf( 0 n );       return 0;     }     for (int i = 1; i <= N; ++i)       for (int j = 0; j < 2; ++j) last[i][j] = -1;     last[1][0] = 0;     while (!q.empty()) {       edge e = q.top();       q.pop();       if (e.l <= e.r) {         if (last[e.v][e.l & 1] >= e.l) {           if (e.u == N) {             printf( %d n , e.l + 1);             return 0;           }           relax(e.u, e.l + 1, e.r + 1);         } else {           adj[e.v][e.l & 1].push_back(e);         }       }     }     printf( -1 n );   }   