#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int N=100010;
typedef pair<int,int> PII;
int q[N],dist[N];
int h[N],e[N],ne[N],w[N],idx;
int n,m;
void add(int a, int b, int c)
{
e[idx]=b, w[idx]=c, ne[idx]=h[a], h[a]=idx++;
}
int dijkstra()
{
memset(dist, 0x3f, sizeof dist);
dist[1]=0;
//堆优化版优先队列
priority_queue <PII, vector<PII>, greater<PII>> heap;//greater小顶堆
heap.push({0,1});//first是距离，second是数字
while(heap.size())
{
auto t=heap.top();//堆用的是top,队列用的是front
heap.pop();
//利用t更新数据
int ver=t.second, distance=t.first;
for(int i=h[ver];i!=-1;i=ne[i])
{
int j=e[i];
if(dist[j]>distance+w[i])
{
dist[j]=distance+w[i];
heap.push({dist[j],j});
}
}
}
if(dist[n]==0x3f3f3f3f) return -1;
return dist[n];
}
int main()
{
cin>>n>>m;
memset(h, -1, sizeof h);
while(m--)
{
int a,b,c;
cin>>a>>b>>c;
add(a,b,c);
}
cout<<dijkstra()<<endl;
return 0;
}
