#include<cstdio>
#include<cstring>
using namespace std;
const int N=200,INF=0x3f3f3f;
int vis[N],d[N];
int g[N][N];
void dijkstra(int s, int n)
 {
    memset(d, INF, sizeof(d));
    memset(vis, 0, sizeof(vis));
    d[s] = 0;
    while(1) {
        int v = -1;
        for(int u = 1; u <= n; u++)
            {
            if(!vis[u] && (v == -1 || d[u] < d[v]))
                v = u;
        }
        if(v == -1)
            break;
        vis[v] = 1;
        for(int u = 1; u <= n; u++)
        {
            if(!vis[u] && d[u] > d[v] + g[v][u]) {
                d[u] = d[v] + g[v][u];

            }
        }
    }

}
int main()
{
    int n,m,a,b,c;
    while(scanf("%d%d",&n,&m)&&m+n!=0)
    {
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=n;j++)
                g[i][j]=g[i][j]=INF;
        }
        for(int i=1;i<=m;i++)
        {
            scanf("%d%d%d",&a,&b,&c);
          g[a][b]=g[b][a]=c;
        }
        dijkstra(1,n);
        printf("%d\n",d[n]);
    }
return 0;
}