// 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;}