#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
const int N = 1000010;
int n,m;
int h[N], e[N], ne[N], idx;
int dis[N], w[N];
bool use[N];
void insert(int a, int b, int c)
{
e[idx] = b;
w[idx] = c;
ne[idx] = h[a];
h[a] = idx++;
}
int dijkstra()
{
memset(dis, 0x3f, sizeof dis);
dis[1] = 0;
priority_queue<pair<int,int>, vector<pair<int,int>>, greater<pair<int,int>>> heap;
heap.push({0,1});
while(heap.size())
{
auto t = heap.top();
heap.pop();
int distance = t.first, num = t.second;
if(use[num]) continue;
use[num] = true;
for(int i = h[num]; i != -1; i = ne[i])
{
int j = e[i];
if(dis[j] > dis[num] + w[i])
{
dis[j] = dis[num] + w[i];
heap.push({dis[j],j});
}
}
}
if(dis[n] == 0x3f3f3f3f) return -1;
else return dis[n];
}
int main()
{
cin >> n >> m;
memset(h, -1, sizeof h);
while(m--)
{
int x, y, z;
cin >> x >> y >> z;
insert(x,y,z);
}
cout << dijkstra();
return 0;
}