最短路//最短路Dijkstra

#include <iostream>
#include <vector>
using namespace std;

const int size = 100+5;
struct edge
{
    int from;
    int to;
    int len;

    int other(int x)
    {
        if(x == from)
            return to;
        else 
            return from;
    }
};

vector<edge> graph[size];//存图
int dis[size];//保存到源点的距离
bool marked[size];

void init(int N)//初始化
{
    for(int i = 1; i <= N; i++)
    {
        graph[i].clear();
        dis[i] = 0x3f3f3f3f;//到源点的距离为无穷大
        marked[i] = false;
    }
}

void Dijkstra(int N)
{
    //先用起始点来初始化
    dis[1] = 0;
    marked[1] = true;
    for(int i = 0; i < graph[1].size(); i++)
    {
        if(graph[1][i].len < dis[graph[1][i].other(1)])
            dis[graph[1][i].other(1)] = graph[1][i].len;
    }
    
    for(int i = 2; i <= N; i++)//还要连N-1个点
    {
        int min = 0x3f3f3f3f;
        int pos;
        for(int i = 1; i <= N; i++)//找最小的未标记的边
        {
            if(!marked[i] && dis[i] < min)
            {
                min = dis[i];
                pos = i;
            }
        }
        marked[pos] = true;
        for(int i = 0; i < graph[pos].size(); i++)//以新点松弛边
        {
            if(dis[pos]+graph[pos][i].len < dis[graph[pos][i].other(pos)])
                dis[graph[pos][i].other(pos)] = dis[pos]+graph[pos][i].len;
        }
    }
}

int main()
{
    int N, M;
    int a, b, c;
    while(cin >> N >> M && N != 0 || M != 0)
    {
        init(N);
        //输入
        for(int i = 0; i < M; i++)
        {
            edge e;
            cin >> e.from >> e.to >> e.len;
            graph[e.from].push_back(e);
            graph[e.to].push_back(e);
        }
        Dijkstra(N);
        printf("%d\n", dis[N]);
    }
    return 0;
}