poj 3162

#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <cctype>
#include <vector>
#include <iterator>
#include <set>
#include <map>
#include <sstream>
using namespace std;

#define mem(a,b) memset(a,b,sizeof(a))
#define pf printf
#define sf scanf
#define spf sprintf
#define pb push_back
#define debug printf("!\n")
#define MAXN 40000+5
#define MAX(a,b) a>b?a:b
#define blank pf("\n")
#define LL long long
#define ALL(x) x.begin(),x.end()
#define INS(x) inserter(x,x.begin())
#define pqueue priority_queue
#define INF 0x3f3f3f3f

#define ls (rt<<1)
#define rs (rt<<1|1)

int n,m;

int head[MAXN],vis[MAXN],ptr=1;

int mx[MAXN],mx2[MAXN],vx[MAXN],vx2[MAXN];

struct node{int y,next,val;}tree[MAXN<<2];

void init()
{
    mem(head,-1);
    mem(vis,0);
    ptr = 1;
}

void add(int son,int fa,int val)
{
    tree[ptr].y=son;
    tree[ptr].val=val;
    tree[ptr].next=head[fa];
    head[fa]=ptr++;
}

void dfs(int root,int fa)
{
    for(int i = head[root];i!=-1;i=tree[i].next)
    {
        int y = tree[i].y;
        if(y==fa) continue;
        dfs(y,root);
        if(mx2[root]<mx[y]+tree[i].val)
        {
            vx2[root] = y;
            mx2[root] = mx[y]+tree[i].val;
            if(mx2[root]>mx[root])
            {
                swap(vx2[root],vx[root]);
                swap(mx2[root],mx[root]);
            }
        }
    }
}

void dfs2(int root,int fa)
{
    for(int i = head[root];i!=-1;i=tree[i].next)
    {
        int y = tree[i].y;
        if(y==fa) continue;
        if(y == vx[root])
        {
            if(mx2[root]+tree[i].val > mx2[y])
            {
                mx2[y] = mx2[root]+tree[i].val;
                vx2[y] = root;
                if(mx2[y]>mx[y])
                {
                    swap(vx2[y],vx[y]);
                    swap(mx2[y],mx[y]);
                }
            }
        }
        else
        {
            if(mx[root]+tree[i].val > mx2[y])
            {
                mx2[y] = mx[root]+tree[i].val;
                vx2[y] = root;
                if(mx2[y]>mx[y])
                {
                    swap(vx2[y],vx[y]);
                    swap(mx2[y],mx[y]);
                }
            }
        }
        dfs2(y,root);
    }
}



int main()
{
    while(~sf("%d%d",&n,&m))
    {
        init();
        for(int i=1;i<n;i++)
        {
            int x,y,z;char ch[2];
            sf("%d%d%d%s",&x,&y,&z,ch);
            add(x,y,z);
            add(y,x,z);
        }
        sf("%d",&K);
        getroot(1,0);
        solve(root);
        pf("%d\n",ans);
    }

}