/*****************************************
Note:
******************************************/
#include <queue>
#include <set>
#include <math.h>
#include <stack>
#include <stdio.h>
#include <iostream>
#include <vector>
#include <iomanip>
#include <string.h>
#include <algorithm>
#include <cstdio>
#include <cstring>
using namespace std;
#define LL long long
const int N = 1e6 + 10;
const int INF = 0x3f3f3f3f;
int n,m,ans,i,j,k;
int head[N],ne[N],to[N],dis[N],w[N],id;
bool vis[N];
void add(int x,int y,int z)
{
	to[++id]=y,w[id]=z,ne[id]=head[x],head[x]=id;
}
struct node{
	int id,num;
	bool operator<(const node &a)const
	{
		return num>a.num;
	}
};
void dij()
{
	priority_queue<node>p;
	p.push((node){1,0});
	p.push((node){n+1,0});
	dis[1]=dis[n+1]=0;
	while(!p.empty())
	{
		node t=p.top();
		p.pop();
		if(vis[t.id]||dis[t.id]!=t.num)
			continue;
		vis[t.id]=1;
		for(int i=head[t.id];i;i=ne[i])
		{
			int v=to[i];
			if(!vis[v]&&dis[v]>dis[t.id]+w[i])
			{
				dis[v]=dis[t.id]+w[i];
				p.push((node){v,dis[v]});
			}
		}
	 } 
}
int main()
{
	memset(dis,0x3f,sizeof vis);
	cin>>n>>m;
	for(int i=1;i<=m;++i)
	{
		int x,y,z;
		cin>>x>>y>>z;
		add(x,y,z);
		add(y+n,x+n,z);
	}
	dij();
	int ans=0;
	for(int i=1;i<=2*n;++i)
		ans+=dis[i];
	cout<<ans;
	return 0;
}

备注：
******************************************/
#include <queue>
#include <math.h>
#include <stack>
#include <stdio.h>
#include <iostream>
#include <vector>
#include <iomanip>
#include <string.h>
#include <algorithm>
#include <map>
using namespace std;
#define LL long long
const int N = 1e6 + 10;
const int INF = 0x3f3f3f3f;
int n, m;
int head[N], ne[N], to[N], w[N], id;
int dis[N], vis[N];
void add(int x, int y, int z)
{
	to[++id] = y, w[id] = z, ne[id] = head[x], head[x] = id;
}
struct node
{
	int id, num;
	bool operator <(const node &a)const
	{
		return num > a.num;
	}
};
void dij()
{
	priority_queue<node> p;
	p.push((node){1, 0});
	p.push((node){n+1, 0});
	dis[1] = dis[n+1] = 0;
	while(!p.empty())
	{
		node t = p.top();
		p.pop();
		if(vis[t.id] || dis[t.id] != t.num)
			continue;
		vis[t.id] = 1;
		for(int i = head[t.id]; i; i = ne[i])
		{
			int v = to[i];
			if(!vis[v] && dis[v] > dis[t.id] + w[i])
			{
				dis[v] = dis[t.id] + w[i];
				p.push((node){v, dis[v]});
			}
		}
	}
}
signed main()
{
	//freopen(".in", "r", stdin);
	//freopen(".out", "w", stdout);
	memset(dis, 0x3f, sizeof dis);
	cin>>n>>m;
	for(int i = 1, x, y, z; i <= m; i++)
	{
		cin>>x>>y>>z;
		add(x, y ,z);
		add(y + n, x + n, z);
	}
	dij();
	int ans = 0;
	for(int i = 1; i <= 2*n; i++)
	{
		ans += dis[i];
	}
	cout<<ans<<endl;
	return 0;
}