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