//hdu1853

 #include<stdio.h>

 #include<string.h>

 #define INF 99999999

 int map[][],pr[],pl[],visr[],visl[],slack[],match[];

 int n,m;

 int dfs(int u)

 {

     int i,j,val;

     visl[u]=;

     for(i=;i<=n;i++)

     {

         if(!visr[i])

         {

             val=pr[i]+pl[u]-map[u][i];

             if(val==)

             {

                 visr[i]=;

                 if(match[i]==-||dfs(match[i]))

                 {

                     match[i]=u;

                     return ;

                 }

             }

             if(val>&&slack[i]>val)

                 slack[i]=val;

         }

     }

     return ;

 }

 void km()

 {

     int i,j,res=,d;

     for(i=;i<=n;i++)

         pl[i]=INF;

     memset(pr,,sizeof(pr));

     memset(match,-,sizeof(match));

     for(i=;i<=n;i++)

     {

         for(j=;j<=n;j++)

             slack[j]=INF;

         while()

         {

             memset(visr,,sizeof(visr));

             memset(visl,,sizeof(visl));

             if(dfs(i))

                 break;

             d=INF;

             for(j=;j<=n;j++)

             {

                 if(!visr[j]&&d>slack[j])

                     d=slack[j];

             }

             for(j=;j<=n;j++)

             {

                 if(visr[j])

                     pr[j]+=d;

                 if(visl[j])

                     pl[j]-=d;

             }

         }

     }

 }

 int main()

 {

     int i,j;

     while(scanf("%d%d",&n,&m)!=EOF)

     {

         for(i=;i<=n;i++)

             for(j=;j<=n;j++)

                 map[i][j]=-INF;

         for(i=;i<m;i++)

         {

             int x,y,z;

             scanf("%d%d%d",&x,&y,&z);

             if(map[x][y]<-z)

             {

                 map[x][y]=-z;

             }

         }

         /*for(i=1;i<=n;i++)

         {

             for(j=1;j<=n;j++)

                 printf("%d ",map[i][j]);

             printf("\n");

         }*/

         km();

         int flag=;

         int res=;

         for(i=;i<=n;i++)

         {

             if(map[match[i]][i]==-INF)

             {flag=;break;}

             else res+=map[match[i]][i];

         }

         if(!flag)printf("-1\n");

         else

          printf("%d\n",-res);

     }

 }