#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
#define INF 1e7 + 2

int n, m;
int w[102][102], d[102], v[102];

void dijkstra(int s){
    memset(v, 0, sizeof(v));
    for(int i=1; i<=n; i++) d[i] = i==s ? 0 : INF;
    for(int i=1; i<=n; i++){
        int x, m = INF;
        for(int y=1; y<=n; y++)
            if(!v[y] && d[y] <= m) m = d[x = y];
        v[x] = 1;
        for(int y=1; y<=n; y++) d[y] = min(d[y], d[x] + w[x][y]);
    }
}

int main(){
//    freopen("in.txt", "r", stdin);
    int x, y, z;
    while(scanf("%d%d", &n, &m)!=EOF){
        if(!n && !m) break;
        for(int i=1; i<=n; i++)
            for(int j=1; j<=i; j++)
                w[i][j] = w[j][i] = i==j ? 0 : INF;
        for(int i=0; i<m; i++){
            scanf("%d%d%d", &x, &y, &z);
            w[x][y] = w[y][x] = min(w[x][y], z);
        }
        dijkstra(1);
        printf("%d\n", d[n]);
    }
    return 0;
}