#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;
const int maxn=200010;
typedef long long ll;
int n,cnt,r1,r2,rt;
ll ans;
int to[maxn<<1],next[maxn<<1],head[maxn];
ll val[maxn<<1],dep[maxn<<1],f[maxn<<1];
inline int rd()
{
	int ret=0,f=1;	char gc=getchar();
	while(gc<‘0‘||gc>‘9‘)	{if(gc==‘-‘)	f=-f;	gc=getchar();}
	while(gc>=‘0‘&&gc<=‘9‘)	ret=ret*10+gc-‘0‘,gc=getchar();
	return ret*f;
}
inline void add(int a,int b,int c)
{
	to[cnt]=b,val[cnt]=c,next[cnt]=head[a],head[a]=cnt++;
}
void dfs(int x,int fa)
{
	if(dep[x]>dep[rt])	rt=x;
	for(int i=head[x];i!=-1;i=next[i])	if(to[i]!=fa)	dep[to[i]]=dep[x]+val[i],dfs(to[i],x);
}
int main()
{
	n=rd(),rd();
	int i,a,b,c;
	memset(head,-1,sizeof(head));
	for(i=1;i<n;i++)	a=rd(),b=rd(),c=rd(),add(a,b,c),add(b,a,c);
	dfs(1,0),r1=rt;
	dep[r1]=0,dfs(r1,0),r2=rt,memcpy(f,dep,sizeof(dep));
	dep[r2]=0,dfs(r2,0);
	for(i=1;i<=n;i++)	ans=max(ans,dep[r1]+min(dep[i],f[i]));
	printf("%lld",ans);
	return 0;
}