#include<iostream>

#include<cstdio>

#include<cstring>

#define re register

using namespace std;

int max(int &a,int &b){return a>b?a:b;}

#define N 50002

int n,m,k,ans,dis[N];

int cnt,hd[N],nxt[N<<],ed[N],poi[N<<],val[N<<];

void adde(int x,int y,int v){

    nxt[ed[x]]=++cnt; hd[x]=hd[x]?hd[x]:cnt;

    ed[x]=cnt; poi[cnt]=y; val[cnt]=v;

}

void dfs(int x,int fa){

    if(dis[x]>dis[k]) k=x;

    for(int i=hd[x];i;i=nxt[i]){

        int to=poi[i];

        if(to==fa) continue;

        dis[to]=dis[x]+val[i];

        dfs(to,x);

    }

}

int main(){

    char c[]; int q1,q2,q3;

    while(~scanf("%d%d",&n,&m)){

        memset(hd,,sizeof(hd));

        memset(ed,,sizeof(ed));

        memset(nxt,,sizeof(nxt));

        ans=cnt=k=;

        for(re int i=;i<n;++i){

            scanf("%d%d%d%s",&q1,&q2,&q3,c);

            adde(q1,q2,q3); adde(q2,q1,q3);

        }

        dis[]=; dfs(,);

        dis[k]=; dfs(k,);

        for(re int i=;i<=n;++i) ans=max(ans,dis[i]);

        printf("%d\n",ans);

    }return ;

}