#include <stdio.h>
#include <string>
#include <string.h>
#include <queue>
#include <stack>
#include <map>
#include <iostream>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
#define inf 0x3f3f3f3f
#define mem0(x , y)  memset(x , y , sizeof(x))
#define ll long long
using namespace std;
struct node{
    int s, e , w ,next ;
} ;
node Edge[100000] ;
int head[50000] , cnt = 0 ;
void add(int s,int e,int w){
    Edge[cnt].s = s ; Edge[cnt].e = e ; Edge[cnt].w = w ; Edge[cnt].next = head[s] ;
    head[s] = cnt ++ ;
}
int dis[100000][3] ;
void dfs(int s , int pre) {
    int f = 0 ;
    int mx = 0 , ms = -1 , mi = -1 ;
    for(int i=head[s] ; i!=-1 ; i=Edge[i].next){
        int v = Edge[i].e ;
        if(pre == v) continue ;
        f ++ ;
        dfs(v, s) ;
        if(mx <= dis[v][0] + Edge[i].w) {
            ms = mx ; mx = dis[v][0] + Edge[i].w ; mi = v ;
        }
    }
    dis[s][0] = mx ; dis[s][1] = ms ; dis[s][2] = mi ;
    ///printf("dfs %d -> %d\n" , s, dis[s][0]) ;
}
int ans = 0 ;
void dfs2(int s,int pre){
    ///printf("%d -> %d\n" , s, dis[s][0]) ;
    ans = max(ans , dis[s][0]) ;
    for(int i=head[s] ; i!=-1 ; i=Edge[i].next){
        int v = Edge[i].e ;
        if(pre == v) continue ;
        if(dis[s][2] == v){
            if(dis[s][0] - Edge[i].w <= Edge[i].w + dis[s][1]){
                dis[v][0] = Edge[i].w + dis[s][1] ;
                dis[v][2] = s ;
            }
        }
        else {
            dis[v][0] = Edge[i].w + dis[s][0] ;
            dis[v][2] = s ;
        }
        dfs2(v , s) ;
    }
}
int main(){
    ///freopen("1" , "r" ,stdin) ;
    int n , m ;
    scanf("%d%d",&n,&m) ;
    mem0(head , -1) ;
    int ta , tb ,tc ;
    char td[4];
    for(int i=0;i<m;i++){
        scanf("%d%d%d%s",&ta,&tb,&tc,td) ;
        add(ta , tb ,tc ) ;
        add(tb , ta ,tc ) ;
    }
    dfs(1 , -1) ;
    dfs2(1 , -1) ;
    printf("%d\n",ans) ;
}