#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<vector>
#include<queue>
#include<deque>
using namespace std;
const int SIZEN=260,INF=0x7fffffff/2;
int len[SIZEN][SIZEN]={0};
vector<int> c[SIZEN];
int N,M;
void SPFA(int S,int T,int f[SIZEN],deque<int> &path,bool type){//若type=1就把结果存放在path中
	bool inq[SIZEN]={0};
	queue<int> Q;
	int pre[SIZEN]={0};
	for(int i=1;i<=N;i++) f[i]=INF;
	f[S]=0,Q.push(S),inq[S]=true;
	while(!Q.empty()){
		int x=Q.front();Q.pop();inq[x]=false;
		for(int i=0;i<c[x].size();i++){
			int u=c[x][i];
			if(f[x]+len[x][u]<f[u]){
				f[u]=f[x]+len[x][u];
				pre[u]=x;
				if(!inq[u]){
					inq[u]=true;
					Q.push(u);
				}
			}
		}
	}
	if(type==1){
		path.clear();
		while(T!=S){
			path.push_front(T);
			T=pre[T];
		}
		path.push_front(S);
	}
}
int f[SIZEN]={0};
deque<int> path;
void work(void){
	SPFA(1,N,f,path,1);
	int mindist=f[N],ans=0;
	for(int i=1;i<path.size();i++){
		int u=path[i-1],v=path[i];
		len[u][v]*=2,len[v][u]*=2;
		SPFA(1,N,f,path,0);
		int nowdist=f[N];
		ans=max(ans,nowdist-mindist);
		len[u][v]/=2,len[v][u]/=2;
	}
	printf("%d\n",ans);
}
void read(void){
	scanf("%d%d",&N,&M);
	int a,b,l;
	for(int i=1;i<=M;i++){
		scanf("%d%d%d",&a,&b,&l);
		len[a][b]=len[b][a]=l;
		c[a].push_back(b),c[b].push_back(a);
	}
}
int main(){
	freopen("rblock.in","r",stdin);
	freopen("rblock.out","w",stdout);
	read();
	work();
	return 0;
}