#include <bits/stdc++.h>
using namespace std;

const int N = 1000010;
int h[N], e[N], ne[N], w[N], idx;
int dist[N];
bool st[N];
int m, n;

void add(int a, int b, int c) {
    w[idx] = c, e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}

int dijkstra() {
    memset(dist,0x3f,sizeof dist);
    dist[1] = 0
 
;
    priority_queue<pair<int,int>> q;
    q.push(make_pair(0,1));
    while(q.size()) {
        auto t = q.top();
        q.pop();
        int ver = t.second;
        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];
                q.push(make_pair(-dist[j],j)); // 加入-dist[j]變為小堆
            }
        }
    }
    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);
    }
    int t = dijkstra();
    printf("%d\n",t);
    return 0;
}