#include<cstdio>

#include<cstring>

#include<algorithm>

#include<cstdlib>

#include<cctype>

#include<queue>

#define maxn 50050

#define maxm 500500

using namespace std;

inline long long read(){

    long long num=,f=;

    char ch=getchar();

    while(!isdigit(ch)){

        if(ch=='-')    f=-;

        ch=getchar();

    }

    while(isdigit(ch)){

        num=num*+ch-'';

        ch=getchar();

    }

    return num*f;

}

struct Edge{

    int from,next,to,vala,valb;

    bool operator <(const Edge a)const{

        return vala<a.vala;

    }

}edge[maxm],d[maxm];

int head[maxn],num;

inline void add(int from,int to,int vala,int valb){

    edge[++num]=(Edge){from,head[from],to,vala,valb};

    head[from]=num;

}

bool vis[maxn];

int dis[maxn];

int n,m;

int spfa(int sta,int stb){

    queue<int>q;    q.push();    q.push(sta);    q.push(stb);

    memset(vis,,sizeof(vis));    vis[]=vis[sta]=vis[stb]=;

    while(!q.empty()){

        int from=q.front();q.pop();    vis[from]=;

        for(int i=head[from];i;i=edge[i].next){

            int to=edge[i].to;

            if(dis[to]<=max(dis[from],edge[i].valb))    continue;

            dis[to]=max(dis[from],edge[i].valb);

            if(vis[to])    continue;

            vis[to]=;    q.push(to);

        }

    }

    return dis[n];

}

int main(){

    freopen("testdata.in.txt","r",stdin);

    n=read(),m=read();

    for(int i=;i<=m;++i)    d[i]=(Edge){read(),,read(),read(),read()};

    sort(d+,d+m+);

    memset(dis,/,sizeof(dis));    dis[]=;

    int ans=0x7fffffff;

    for(int i=;i<=m;++i){

        add(d[i].from,d[i].to,d[i].vala,d[i].valb);

        add(d[i].to,d[i].from,d[i].vala,d[i].valb);

        int now=d[i].vala+spfa(d[i].from,d[i].to);

        if(now<ans)    ans=now;

    }

    printf("%d\n",ans==?-:ans);

    return ;

}