1 #include <map>  2 #include <set>  3 #include <stack>  4 #include <queue>  5 #include <cmath>  6 #include <ctime>  7 #include <string>  8 #include <vector>  9 #include <cstdio> 10 #include <cstdlib> 11 #include <cstring> 12 #include <cassert> 13 #include <iostream> 14 #include <algorithm> 15 #pragma comment(linker,"/STACK:102400000,102400000") 16 using namespace std; 17  18 #define N 200008              19 #define E 400008     20 #define LL long long 21 #define lson l,m,rt<<1 22 #define rson m+1,r,rt<<1|1  23 #define clr(x,v) memset(x,v,sizeof(x)); 24 #define bitcnt(x) __builtin_popcount(x) 25 #define rep(x,y,z) for (int x=y;x<=z;x++) 26 #define repd(x,y,z) for (int x=y;x>=z;x--) 27 const int mo  = 1000000007; 28 const int inf = 0x3f3f3f3f; 29 const int INF = 2000000000; 30 /**************************************************************************/  31 int n,m; 32 int fa[N],val[N],mx[N],rev[N],c[N][2],st[N]; 33  34 struct line{ 35     int u,v,a,b; 36     bool operator < (const line &k) const{ 37         return a<k.a; 38     } 39 }eg[E]; 40 bool isroot(int k){ 41     return c[fa[k]][0]!=k && c[fa[k]][1]!=k; 42 } 43 void pushup(int x){ 44     int l=c[x][0],r=c[x][1]; 45     mx[x]=x; 46     if  (val[mx[l]]>val[mx[x]]) mx[x]=mx[l]; 47     if  (val[mx[r]]>val[mx[x]]) mx[x]=mx[r]; 48 } 49 void pushdown(int x){ 50     int l=c[x][0],r=c[x][1]; 51     if (rev[x]){ 52         if (l) rev[l]^=1; 53         if (r) rev[r]^=1; 54         rev[x]^=1; 55         swap(c[x][0],c[x][1]); 56     } 57 } 58 void rotate(int x){ 59     int y=fa[x],z=fa[y],l,r; 60     if (c[y][0]==x) l=0; else l=1; r=l^1; 61     if (!isroot(y)){ 62         if (c[z][0]==y) c[z][0]=x; else c[z][1]=x; 63     } 64     fa[x]=z; fa[y]=x; fa[c[x][r]]=y; 65     c[y][l]=c[x][r]; c[x][r]=y; 66     pushup(y); pushup(x); 67 } 68 void splay(int x){ 69     int top=0; st[++top]=x; 70     for (int i=x;!isroot(i);i=fa[i]) st[++top]=fa[i]; 71     while (top) pushdown(st[top--]); 72     while (!isroot(x)){ 73         int y=fa[x],z=fa[y]; 74         if (!isroot(y)){ 75             if (c[y][0]==x^c[z][0]==y) rotate(x); 76             else rotate(y); 77         } 78         rotate(x); 79     } 80 } 81 void access(int x){ 82     int t=0; 83     while (x){ 84         splay(x); 85         c[x][1]=t; 86         pushup(x); 87         t=x; x=fa[x]; 88     } 89 } 90 void rever(int x){ 91     access(x); splay(x); rev[x]^=1; 92 } 93 void link(int u,int v){ 94     rever(u); fa[u]=v; 95 } 96 void cut(int u,int v){ 97     rever(u); access(v); splay(v); fa[c[v][0]]=0; c[v][0]=0; pushup(v); 98 } 99 int find(int u){100     access(u); splay(u);101     while (c[u][0]) u=c[u][0];102     return u;103 }104 int query(int u,int v){105     rever(u); access(v); splay(v); return mx[v];106 }107 108 int main(){109     scanf("%d%d",&n,&m);110     rep(i,1,m) scanf("%d%d%d%d",&eg[i].u,&eg[i].v,&eg[i].a,&eg[i].b);111     sort(eg+1,eg+m+1);112     int ans=INF;113     rep(i,1,m){114         int u=eg[i].u,v=eg[i].v,a=eg[i].a,b=eg[i].b;115         int flag=1;116         if (find(u)==find(v)){117             int t=query(u,v);118             if (b<val[t]){119                 cut(t,eg[t-n].u);120                 cut(t,eg[t-n].v);121             }122             else flag=0;123         }124         if (flag) {125             val[i+n]=b; mx[n+i]=n+i;126             link(i+n,u); 127             link(i+n,v);128         }129         if (find(1)==find(n)){130             int t=query(1,n);131             ans=min(ans,val[t]+a);132         }133     }134     printf("%d\n",ans==INF?-1:ans);135 }