#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
typedef pair<int,int> PII;
const int N=1e6+10;
int n,m;
int e[N],h[N],ne[N],w[N],dist[N],idx;
bool st[N];
void add(int a, int b, int c)
{
e[idx]=b,ne[idx]=h[a],w[idx]=c,h[a]=idx++;
}
int dijstra()
{
memset(dist,0x3f,sizeof dist);
dist[1]=0;
priority_queue<PII,vector<PII>,greater<PII>> heap;
heap.push({0,1});
while(!heap.empty())
{
auto t=heap.top();heap.pop();
int ver=t.second;
if(st[ver])continue;
st[ver]=true;
for(int j=h[ver];j!=-1;j=ne[j])
{
int i=e[j];
if(dist[i] > dist[ver] + w[j])
{
dist[i]=dist[ver]+w[j];
heap.push({dist[i],i});
}
}
}
if(dist[n]==0x3f3f3f3f) return -1;
return dist[n];
}
int main()
{
cin>>n>>m;
memset(h,-1,sizeof h);
for(int i=0;i<m;++i)
{
int a,b,c;
scanf("%d%d%d",&a,&b,&c);
add(a,b,c);
}
cout<<dijstra()<<endl;
return 0;
}