//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<sstream>
#include<cmath>
#include<climits>
#include<string>
#include<map>
#include<queue>
#include<vector>
#include<stack>
#include<set>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
#define pb(a) push(a)
#define INF 0x1f1f1f1f
#define lson idx<<1,l,mid
#define rson idx<<1|1,mid+1,r
#define PI  3.1415926535898
template<class T> T min(const T& a,const T& b,const T& c) {return min(min(a,b),min(a,c));
}
template<class T> T max(const T& a,const T& b,const T& c) {return max(max(a,b),max(a,c));
}
void debug() {
#ifdef ONLINE_JUDGE
#elsefreopen("in.txt","r",stdin);//freopen("d:\\out1.txt","w",stdout);
#endif
}
int getch() {int ch;while((ch=getchar())!=EOF) {if(ch!=' '&&ch!='\n')return ch;}return EOF;
}struct HeapNode
{int d,u;bool operator < (const HeapNode &ant) const{return ant.d<d;}
};struct Edge
{int from,to,dist;
};const int maxn=5005;vector<int> g[maxn];
vector<Edge> edge;
int n;
int d1[maxn],d2[maxn];void init()
{for(int i=1;i<=n;i++)g[i].clear();edge.clear();
}void add(int u,int v,int w)
{Edge e=(Edge){u,v,w};edge.push_back(e);g[u].push_back(edge.size()-1);
}
void solve(int s)
{for(int i=1;i<=n;i++)d1[i]=d2[i]=INF;priority_queue<HeapNode> q;d1[s]=0;q.push((HeapNode){0,s});while(!q.empty()){HeapNode x=q.top(); q.pop();if(x.d>d2[x.u])continue;int u=x.u;for(int i=0;i<g[u].size();i++){Edge &e=edge[g[u][i]];int v=e.to;int d=x.d;if(e.dist+d<d1[v]){d2[v]=d1[v];d1[v]=d+e.dist;q.push((HeapNode){d1[v],v});}else if(e.dist+d<d2[v]&&e.dist+d!=d1[v]){d2[v]=d+e.dist;q.push((HeapNode){d2[v],v});}}}
}
int main()
{int m;while(scanf("%d%d",&n,&m)!=EOF){init();for(int i=1;i<=m;i++){int u,v,w;scanf("%d%d%d",&u,&v,&w);add(u,v,w);add(v,u,w);}solve(1);printf("%d\n",d2[n]);}return 0;
}