#include<stdio.h>
#include<string.h>
#define mmax 101
const int INF = 1000000000;
int v[mmax],d[mmax],w[mmax][mmax];
int main()
{
    int i,j,k,n,m;
    int a,b,c;

    while(~scanf("%d%d",&n,&m),n+m)
    {
        memset(v, 0, sizeof(v));
        memset(w, 0, sizeof(w));
        for(i=1; i<=m; i++)
        {
            scanf("%d%d%d",&a,&b,&c);
            w[a][b] = c;
            w[b][a] = c;
        }
        for(i=1; i<=n; i++)
            d[i] = (i==1 ? 0 : INF);
        for(i=1; i<=n; i++)
        {
            int mmin = INF;
            for(j=1; j<=n; j++)
                if(!v[j] && d[j]<=mmin)
                   mmin = d[k=j];
            v[k] = 1;
            for(j=1; j<=n; j++)
                if(!v[j] && w[k][j]!=0 && d[k]+w[k][j]<d[j])
                   d[j] = d[k] + w[k][j];
        }
        printf("%d\n",d[n]);
    }
    return 0;
}