#include <cstdio>
#include <cstring>
#include <queue>
#define max(a, b) (a > b ? a : b)
using namespace std;
const int N = 1e5 + 5, M = 1e5 + 5, INF = 0x3f3f3f3f;
struct E {
    int v, w, next;
}e[M];
struct Node {
    int v, d;
    Node(int v, int d):v(v), d(d){}
    bool operator < (const Node &w)const {
        return d > w.d;
    }
};
int n, m, len = 1, head[N], d[N];
bool vis[N];
void add(int u, int v, int w) {
    e[len].v = v;
    e[len].next = head[u];
    e[len].w = w;
    head[u] = len++;
}
void dijkstra(int u) {
    memset(d, 0x3f, sizeof(d));
    d[u] = 0;
    priority_queue<Node> q; 
    q.push(Node(u, 0));
    while (!q.empty()) {
        u = q.top().v;
        q.pop();
        if (vis[u]) continue;
        vis[u] = true;
        for (int j = head[u]; j; j = e[j].next) {
            int v = e[j].v;
            int w = e[j].w;
            if (!vis[v] && d[v] > d[u] + w) {
                d[v] = d[u] +w;
                q.push(Node(v, d[v]));
            }
        }
    }
}
int main() {
    scanf("%d%d", &n, &m);
    int u, v, w;
    for (int i = 1; i <= m; i++) {
        scanf("%d%d%d", &u, &v, &w);
        add(u, v, w);
    }
    dijkstra(1);
    printf("%d\n", d[n] == INF ? -1 : d[n]);
    return 0;
}