public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int N = sc . nextInt ( ) ;
  int M = sc . nextInt ( ) ;
  long [ ] [ ] v = new long [ N ] [ N ] ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    for ( int j = 0 ;
    j < N ;
    j ++ ) {
      if ( i != j ) {
        v [ i ] [ j ] = INF ;
      }
    }
  }
  for ( int i = 0 ;
  i < M ;
  i ++ ) {
    int u1 = sc . nextInt ( ) - 1 ;
    int u2 = sc . nextInt ( ) - 1 ;
    int l = sc . nextInt ( ) ;
    v [ u1 ] [ u2 ] = l ;
    v [ u2 ] [ u1 ] = l ;
  }
  for ( int k = 1 ;
  k < N ;
  k ++ ) {
    for ( int i = 1 ;
    i < N ;
    i ++ ) {
      for ( int j = 1 ;
      j < N ;
      j ++ ) {
        v [ i ] [ j ] = Math . min ( v [ i ] [ j ] , v [ i ] [ k ] + v [ k ] [ j ] ) ;
      }
    }
  }
  long ans = INF ;
  for ( int i = 1 ;
  i < N ;
  i ++ ) {
    for ( int j = 1 ;
    j < N ;
    j ++ ) {
      if ( i == j ) {
        continue ;
      }
      long sum = v [ i ] [ j ] + v [ 0 ] [ i ] + v [ 0 ] [ j ] ;
      ans = Math . min ( ans , sum ) ;
    }
  }
  System . out . println ( ans < INF ? ans : - 1 ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int N = sc . nextInt ( ) ; int M = sc . nextInt ( ) ; long [ ] [ ] v = new long [ N ] [ N ] ; for ( int i = 0 ; i < N ; i ++ ) { for ( int j = 0 ; j < N ; j ++ ) { if ( i != j ) { v [ i ] [ j ] = INF ; } } } for ( int i = 0 ; i < M ; i ++ ) { int u1 = sc . nextInt ( ) - 1 ; int u2 = sc . nextInt ( ) - 1 ; int l = sc . nextInt ( ) ; v [ u1 ] [ u2 ] = l ; v [ u2 ] [ u1 ] = l ; } for ( int k = 1 ; k < N ; k ++ ) { for ( int i = 1 ; i < N ; i ++ ) { for ( int j = 1 ; j < N ; j ++ ) { v [ i ] [ j ] = Math . min ( v [ i ] [ j ] , v [ i ] [ k ] + v [ k ] [ j ] ) ; } } } long ans = INF ; for ( int i = 1 ; i < N ; i ++ ) { for ( int j = 1 ; j < N ; j ++ ) { if ( i == j ) { continue ; } long sum = v [ i ] [ j ] + v [ 0 ] [ i ] + v [ 0 ] [ j ] ; ans = Math . min ( ans , sum ) ; } } System . out . println ( ans < INF ? ans : - 1 ) ; }
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