Source Code
#include<queue>
#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int MAXN = 100000;
const int MAXM = 100000;
const int INF = 1999999999;
struct Edge
{
 int to,next,cap,flow,cost;
}edge[MAXM];
int head[MAXN],tol;
int pre[MAXN],dis[MAXN];
bool vis[MAXN];
int N;//节点总个数，节点编号从0~N-1
void init(int n)
{
 N = n;
 tol = 0;
 memset(head,-1,sizeof(head));
}
void addedge(int u,int v,int cap,int cost)
{
 edge[tol].to = v;
 edge[tol].cap = cap;
 edge[tol].cost = cost;
 edge[tol].flow = 0;
 edge[tol].next = head[u];
 head[u] = tol++;
 edge[tol].to = u;
 edge[tol].cap = 0;
 edge[tol].cost = -cost;
 edge[tol].flow = 0;
 edge[tol].next = head[v];
 head[v] = tol++;
}
bool spfa(int s,int t)
{
 queue<int>q;
 for(int i = 0;i <= N;i++)
 {
 dis[i] = INF;
 vis[i] = false;
 pre[i] = -1;
 }
 dis[s] = 0;
 vis[s] = true;
 q.push(s);
 while(!q.empty())
 {
 //cout<<1<<endl;
 int u = q.front();
 q.pop();
 vis[u] = false;
 for(int i = head[u]; i != -1;i = edge[i].next)
 {
 int v = edge[i].to;
 if(edge[i].cap > edge[i].flow &&
 dis[v] > dis[u] + edge[i].cost )
 {
 dis[v] = dis[u] + edge[i].cost;
 pre[v] = i;
 if(!vis[v])
 {
 vis[v] = true;
 q.push(v);
 }
 }
 }
 }
 if(pre[t] == -1)return false;
 else return true;
}
//返回的是最大流，cost存的是最小费用
int minCostMaxflow(int s,int t,int &cost)
{
 int flow = 0;
 cost = 0;
 while(spfa(s,t))
 {
 //cout<<1<<endl;
 int Min = INF;
 for(int i = pre[t];i != -1;i = pre[edge[i^1].to])
 {
 if(Min > edge[i].cap - edge[i].flow)
 Min = edge[i].cap - edge[i].flow;
 }
 for(int i = pre[t];i != -1;i = pre[edge[i^1].to])
 {
 edge[i].flow += Min;
 edge[i^1].flow -= Min;
 cost += edge[i].cost * Min;
 }
 flow += Min;
 }
 return flow;
}
int main()
{
	int n,m;
	while(cin>>n>>m)
	{
		init(n+1);
		int u,v,w,s,t;
		while(m--)
		{
			cin>>u>>v>>w;
			addedge(u,v,1,w);
			addedge(v,u,1,w);
		}
		addedge(0,1,2,0);
		addedge(n,n+1,2,0);
		int cost;
		int ans=minCostMaxflow(0,n+1,cost);
		cout<<cost<<endl;
	}
}