#include<cstring>
#include<iostream>
#include<algorithm>
#include<queue>
using namespace std;
typedef pair<int,int> PII;
const int N=1e6+10;
int n,m,h[N],w[N],e[N],ne[N],idx,dist[N];
bool st[N];
void add1(int a,int b,int c)
{
e[idx]=b,w[idx]=c,ne[idx]=h[a],h[a]=idx++;
}
int dijkstra()
{
int ver,i,j;
memset(dist,0x3f,sizeof(dist));
dist[1]=0;
priority_queue<PII,vector<PII>,greater<PII>>heap;
heap.push(make_pair(0,1));
while(heap.size()){
auto t=heap.top();
heap.pop();
ver=t.second,distance=t.first;
if(st[ver])continue;
st[ver]=true;
for(i=h[ver];i!=-1;i=ne[i]){
j=e[i];
if(dist[j]>dist[ver]+w[i]){
dist[j]=dist[ver]+w[i];
heap.push(make_pair(dist[j],j));
}
}
}
if (dist[n] == 0x3f3f3f3f) return -1;
return dist[n];
}
int main()
{
int a,b,c;
scanf("%d%d",&n,&m);
memset(h,-1,sizeof(h);
while(m--){
scanf("%d%d%d",&a,&b,&c);
add1(a,b,c);
}
printf("%d\n",dijkstra());
return 0;
}
加油!