2 1
1 2 3
3 3
1 2 5
2 3 5
3 1 2
0 0

3
2

#include <bits/stdc++.h>
//#pragma comment(linker, "/STACK:102400000, 102400000")
using namespace std;
const int maxn = 105;
const int inf = 0x3f3f3f3f;
int w[maxn][maxn], d[maxn];
bool vis[maxn];
int n, m;

void dijkstra(){
	memset(vis, false, sizeof(bool)*(n+1));
	for (int i=1; i<=n; ++i)
		d[i] = (i==1 ? 0 : inf);
	for (int i=1; i<=n; ++i){
		int x=0, m=inf;
		for (int y=1; y<=n; ++y)
			if (!vis[y] && d[y]<=m)
				m = d[x=y];
		vis[x] = true;
		for (int y=1; y<=n; ++y)
			d[y] = min(d[y], d[x]+w[x][y]);
	}
}

int main(){
	#ifdef LOCAL
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
	#endif
	while (~scanf("%d%d", &n, &m) && n+m){
		int x, y, c;
		for (x=1; x<=n; ++x)
			for (y=1; y<=n; ++y)
				w[x][y] = (x==y ? 0 : inf);
		for (int i=1; i<=m; ++i){
			scanf("%d%d%d", &x, &y, &c);
			w[x][y] = w[y][x] = c;
		}
		dijkstra();
		printf("%d\n", d[n]);
	}
	return 0;
}