C++ :

#include <cstdio>
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <ctime>
#include <climits>
#include <set>
#include <map>
#include <queue>
using namespace std;
int n,m;
struct NODE{
	int to;
	int next;
	int va;
}A[2005];
int len=0;
int head[1005];
bool exist[1005];
int dis[1005];
int my_max=0;
queue<int>T;
void Build(int a,int b,int c){
	len++;
	A[len].to=b;
	A[len].va=c;
	A[len].next=head[a];
	head[a]=len;
}
void init(){
	scanf("%d%d",&n,&m);
	int a,b,c;
	for(int i=1;i<=m;i++){
//		cout<<a<<" "<<b<<endl;
		scanf("%d%d%d",&a,&b,&c);
		Build(a,b,c);
		Build(b,a,c);
	}
}
void SPFA(int x,int tot){
	my_max=my_max>tot? my_max:tot;
	for(int i=head[x];i;i=A[i].next){
		int y=A[i].to;
		if(exist[y]==false)exist[y]=true,SPFA(y,tot+A[i].va);
	}
	exist[x]=false;
}
void work(){
	for(int i=1;i<=n;i++){
		exist[i]=true;
		SPFA(i,0);
		exist[i]=false;
//		memset(exist,0,sizeof(exist));
	}
	printf("%d\n",my_max);
}
int main(){
//    freopen("1.in","r",stdin);
    //freopen("walk.in","r",stdin);
   // freopen("walk.out","w",stdout);
	init();
	work();
//	cout<<(double)clock() / CLOCKS_PER_SEC<<endl;
//	while(1);
    fclose(stdin);
    fclose(stdout);
}