cogs 1685 魔法森林

/*
    写了个傻逼二分套二分，真的傻逼了，我这tmd是在贪心呐，70分满满的人品
*/
#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#define maxn 50010
using namespace std;
int head[maxn],num,n,m,mx1,mx2,mid1,mid2,ans=0x7fffffff;
bool vis[maxn],ok[];
struct node{int to,pre,v1,v2;}e[];
struct Node{int from,to,v1,v2;}edge[];
void Insert(int from,int to,int v1,int v2){
    e[++num].to=to;
    e[num].v1=v1;
    e[num].v2=v2;
    e[num].pre=head[from];
    head[from]=num;
}
void bfs(){
    queue<int>q;
    q.push();vis[]=;
    while(!q.empty()){
        int now=q.front();q.pop();
        for(int i=head[now];i;i=e[i].pre){
            int to=e[i].to;
            if(!vis[to]){vis[to]=;q.push(to);}
        }
    }
}
bool check1(){
    memset(vis,,sizeof(vis));
    memset(ok,,sizeof(ok));
    memset(head,,sizeof(head));num=;
    for(int i=;i<=m;i++){
        if(edge[i].v1>mid1)continue;
        Insert(edge[i].from,edge[i].to,edge[i].v1,edge[i].v2);
        Insert(edge[i].to,edge[i].from,edge[i].v1,edge[i].v2);
        ok[i]=;
    }
    bfs();
    return vis[n];
}
bool check2(){
    memset(vis,,sizeof(vis));
    memset(head,,sizeof(head));num=;
    for(int i=;i<=m;i++){
        if((edge[i].v2>mid2)||(!ok[i]))continue;
        Insert(edge[i].from,edge[i].to,edge[i].v1,edge[i].v2);
        Insert(edge[i].to,edge[i].from,edge[i].v1,edge[i].v2);
    }
    bfs();
    return vis[n];
}
int main(){
    freopen("magicalforest11.in","r",stdin);//freopen("magicalforest.out","w",stdout);
    scanf("%d%d",&n,&m);
    int x,y,z,c;
    for(int i=;i<=m;i++){
        scanf("%d%d%d%d",&x,&y,&z,&c);
        edge[i].from=x;edge[i].to=y;edge[i].v1=z;edge[i].v2=c;
        Insert(x,y,z,c);Insert(y,x,z,c);
        mx1=max(mx1,z);
        mx2=max(mx2,c);
    }
    bfs();
    if(!vis[n]){puts("-1");return ;}
    int l1=,r1=mx1;
    while(l1<=r1){
        mid1=(l1+r1)>>;
        if(check1()){
            int l2=,r2=mx2;
            while(l2<=r2){
                mid2=(l2+r2)>>;
                if(check2())r2=mid2-,ans=min(ans,mid1+mid2);
                else l2=mid2+;
            }
            r1=mid1-;
        }
        else l1=mid1+;
    }
    printf("%d",ans);
    return ;
}