uva1658

/* solution:                    ，        ， 2~v-1       i i‘          1   0      。   1～v    2        note:     date: 2016/4/24 */
#include <iostream>
#include <cstdio>
#include <vector>
#include <queue>
#include <algorithm>
#include <cstring>

using namespace std;
const int maxn = 2000 + 10;
const int INF = 1000000000;

int n, m;

struct Edge {
  int from, to, cap, flow, cost;
  Edge(int u, int v, int c, int f, int w):from(u),to(v),cap(c),flow(f),cost(w) {}
};

struct MCMF {
  int n, m;
  vector<Edge> edges;
  vector<int> G[maxn];
  int inq[maxn];         //       
  int d[maxn];           // Bellman-Ford
  int p[maxn];           //     
  int a[maxn];           //     

  void init(int n) {
    this->n = n;
    for(int i = 0; i < n; i++) G[i].clear();
    edges.clear();
  }

  void AddEdge(int from, int to, int cap, int cost) {
    edges.push_back(Edge(from, to, cap, 0, cost));
    edges.push_back(Edge(to, from, 0, 0, -cost));
    m = edges.size();
    G[from].push_back(m-2);
    G[to].push_back(m-1);
  }

  bool BellmanFord(int s, int t, int flow_limit, int& flow, int& cost) {
    for(int i = 0; i < n; i++) d[i] = INF;
    memset(inq, 0, sizeof(inq));
    d[s] = 0; inq[s] = 1; p[s] = 0; a[s] = INF;

    queue<int> Q;
    Q.push(s);
    while(!Q.empty()) {
      int u = Q.front(); Q.pop();
      inq[u] = 0;
      for(int i = 0; i < G[u].size(); i++) {
        Edge& e = edges[G[u][i]];
        if(e.cap > e.flow && d[e.to] > d[u] + e.cost) {
          d[e.to] = d[u] + e.cost;
          p[e.to] = G[u][i];
          a[e.to] = min(a[u], e.cap - e.flow);
          if(!inq[e.to]) { Q.push(e.to); inq[e.to] = 1; }
        }
      }
    }
    if(d[t] == INF) return false;
    if(flow + a[t] > flow_limit) a[t] = flow_limit - flow;
    flow += a[t];
    cost += d[t] * a[t];
    for(int u = t; u != s; u = edges[p[u]].from) {
      edges[p[u]].flow += a[t];
      edges[p[u]^1].flow -= a[t];
    }
    return true;
  }

  //               
  int MincostFlow(int s, int t, int flow_limit, int& cost) {
    int flow = 0; cost = 0;
    while(flow < flow_limit && BellmanFord(s, t, flow_limit, flow, cost));
    return flow;
  }

};

MCMF g;

int main()
{
    //freopen("input.txt", "r", stdin);
    while(scanf("%d%d", &n, &m) == 2 && n) {
        g.init(2 * n - 2);
        for(int i = 2; i <= n - 1; i++)
            g.AddEdge(i - 1, i + n - 2, 1, 0);

        int a, b, val;
        while(m--) {
            scanf("%d%d%d", &a, &b, &val);
            if(a != 1 && a != n)
                a += n - 2;
            else
                a--;
            b--;

            g.AddEdge(a, b, 1, val);
        }

        int cost = 0;
        g.MincostFlow(0, n-1, 2, cost);
        printf("%d
", cost);
    }
    return 0;
}