#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 510;

int g[N][N];
int n, m;
int dist[N];
bool st[N];

int dijkstra(){
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;
    
	//遍歷所有點
    for(int i = 1; i <= n; i ++){
		//找出不在集合中的最近的點加入集合
        int t = -1;  //技巧性寫法
        for(int j = 1; j <= n; j ++){
            if(!st[j] && (dist[t] > dist[j] || t == -1)){
                t = j;
            }
        }
		//用這個點更新其他點的距離
        for(int j = 1; j <= n; j ++){
            if(dist[j] > dist[t] +g[t][j]){
                dist[j] = dist[t] + g[t][j];
            }
        }
		//將這個點加入集合
        st[t] = true;
    }
    if(dist[n] == 0x3f3f3f3f) return -1;
    return dist[n];
}

int main()
{
    scanf("%d%d", &n, &m);
    memset(g, 0x3f, sizeof g);
    while(m --){
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        g[a][b] = min(g[a][b], c);
    }
    printf("%d\n", dijkstra());
    
    return 0;
}
 

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>

using namespace std;

typedef pair<int, int> PII;

const int N = 2e5 + 10;

int n, m;
int h[N], e[N], ne[N], w[N], idx;
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;
    
	//堆的定義
    priority_queue<PII, vector<PII>, greater<PII>> heap;
    heap.push({0, 1});
    
    while(!heap.empty()){
        PII t = heap.top();
        heap.pop();
        
		//找到不在集合中的最近的點，將它加入集合
		//由於PII預設按照第一維排序，所以PII的第一維存distance
        int ver = t.second, distance = t.first;
        if(st[ver]) continue;
        st[ver] = true;
        
		//更新其他所有點的距離
        for(int i = h[ver]; i != -1; i = ne[i]){
            int j = e[i];
            if(dist[j] > distance + w[i]){
                dist[j] = distance + 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);
    }
    printf("%d\n", dijkstra());
    
    return 0;
}