#include<bits/stdc++.h>
#define int long long
#define sfor(i,j,k) for(register int i=j;i<=k;++i)
#define dfor(i,j,k) for(register int i=k;i>=j;--i)
using namespace std;
int n,m,cnt,head[1000005],dis[2005][2005],a,b,c;
priority_queue<pair<int,int>,vector<pair<int,int> >,greater<pair<int,int> > >q;
struct node{
    int u,v,w,nxt;
}e[200005];
void u(int u,int v,int w){
    e[++cnt].v = v;
	e[cnt].u=u;
    e[cnt].w = w;
    e[cnt].nxt = head[u];
    head[u] = cnt;
}
bool vis[2003];
void dijkstra(int s){
    memset(vis,0,sizeof(vis));
    dis[s][s]=0;
    q.push(make_pair(0,s));
    while(!q.empty()){
        int x=q.top().second;
        q.pop();
        if(vis[x]) continue;
        vis[x]=1;
        for(int i = head[x];i;i = e[i].nxt)
        {
            int v = e[i].v;
            int w = e[i].w;
            if(dis[s][v] > max(dis[s][x] + w,0ll))
            {
                dis[s][v] = max(dis[s][x] + w,0ll);
                q.push(make_pair(dis[s][v],v));
            }
        }
    }
}
signed main(){
    memset(dis,0x3f3f3f3f,sizeof(dis));
    cin>>n>>m;
    for(int i=1;i<=m;i++){
        cin>>a>>b>>c;
        u(a,b,c);
    }
    for(int i=1;i<=n;i++)
      dijkstra(i);
    int ans=dis[1][n];
    for(int i=1;i<=m;i++)
      if(e[i].w+dis[e[i].u][e[i].v]<0&&(dis[n][e[i].u]<dis[0][0]||dis[1][e[i].u]<dis[0][0]))
        ans=min(ans,dis[e[i].v][n]);
    cout<<max(0ll,ans)<<endl;
    return 0;
}