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| #include<bits/stdc++.h>
using namespace std;
#define il inline
#define rg register
//#define int long long
il int read()
{
int re=0,k=1;char ch=getchar();
while(ch>'9'||ch<'0'){if(ch=='-')k=-1;ch=getchar();}
while(ch<='9'&&ch>='0'){re=re*10+ch-48;ch=getchar();}
return re*k;
}
il void write(int x)
{
if(x<0)return putchar('-'),write(-x),void();
if(x<10)return putchar(x+'0'),void();
return write(x/10),putchar(x%10+'0'),void();
}
const int B=800;
int n,m,ans;
struct ss{
int u,v,a,b;
bool operator <(const ss ot)const{
return a<ot.a;
}
}e[10000005];
struct st{
int u,v,b;
bool operator <(const st ot)const{
return b<ot.b;
}
}now[10000005];
int fa[10000005],sz[10000005],s[10000005],ls,lnow,las;
bool vis[10000005];
void merge(int u,int v)
{
if(u==v)return;
if(sz[u]>sz[v])swap(u,v);
fa[u]=v;
sz[v]+=sz[u];
s[++ls]=u;
}
int find(int x)
{
if(x==fa[x])return x;
return find(fa[x]);
}
void redo()
{
sz[fa[s[ls]]]-=sz[s[ls]];
fa[s[ls]]=s[ls];
ls--;
}
bool pd(int x)
{
redo();
lnow--;
int t=ls;
for(rg int i=las;i<=x;i++)
{
if(e[i].b>now[lnow].b)continue;
merge(find(e[i].u),find(e[i].v));
}
if(find(n)==find(1)){while(ls>t)redo();return 1;}
while(ls>t)redo();
lnow++;
merge(find(now[lnow].u),find(now[lnow].v));
return 0;
}
void init()
{
for(rg int i=1;i<=n;i++)
fa[i]=i,sz[i]=1;
}
void build()
{
init();
for(rg int i=1;i<=lnow;i++)
{
if(find(now[i].u)!=find(now[i].v))vis[i]=1;
else vis[i]=0;
merge(find(now[i].u),find(now[i].v));
}
}
signed main()
{
n=read();m=read();
for(rg int i=1;i<=m;i++)
{
e[i].u=read();e[i].v=read();
e[i].a=read();e[i].b=read();
}
sort(e+1,e+m+1);
init();
ans=0x3f3f3f3f;
int st=1;
init();
while(find(1)!=find(n)&&st<=m)
{
now[++lnow].u=e[st].u;
now[lnow].v=e[st].v;
now[lnow].b=e[st].b;
merge(find(e[st].u),find(e[st].v));
st++;
}
sort(now+1,now+lnow+1);
build();
las=st;
do
{
while(!vis[lnow]&&lnow)
lnow--;
}
while(pd(st-1));
if(find(1)==find(n))
{
ans=e[st-1].a+now[lnow].b;
}
for(rg int i=st;i<=m&&lnow>0;i++)
{
do
{
while(!vis[lnow]&&lnow)
lnow--;
}
while(pd(i));
if(lnow>0)
ans=min(ans,e[i].a+now[lnow].b);
if(i-las+1==B)
{
int t=lnow;
for(rg int j=las;j<=i;j++)
{
if(e[j].b>now[t].b)continue;
now[++lnow].u=e[j].u;
now[lnow].v=e[j].v;
now[lnow].b=e[j].b;
}
las=i+1;
sort(now+1,now+lnow+1);
build();
}
}
if(ans==0x3f3f3f3f)
ans=-1;
write(ans);
}
|