// poj1985

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstring>

#include<cstdio>

#include<cmath>

#define LL long long

#define MOD 100000000

#define inf 2147483640

#define Pi acos(-1.0)

#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);

using namespace std;

const int maxn=40010;

struct edge {int to,next,w;}e[maxn<<1];

int n,m,rt,ans,cnt,head[maxn];

void link(int u,int v,int w) {

	e[++cnt].to=v;e[cnt].next=head[u];head[u]=cnt;e[cnt].w=w;

	e[++cnt].to=u;e[cnt].next=head[v];head[v]=cnt;e[cnt].w=w;

}

void dfs(int x,int fa,int d) {

	if (ans<d) ans=d,rt=x;

	for (int i=head[x];i;i=e[i].next)

		if (e[i].to!=fa) dfs(e[i].to,x,d+e[i].w);

}

int main() {

	scanf("%d%d",&n,&m);

	char ch;

	for (int u,v,w,i=1;i<=m;i++) {

		scanf("%d%d%d %c",&u,&v,&w,&ch);

		link(u,v,w);

	}

	rt=ans=0;dfs(1,0,0);

	dfs(rt,0,0);

	printf("%d",ans);

	return 0;

}