public static void main ( String [ ] args ) {
  FastScanner sc = new FastScanner ( ) ;
  PrintWriter pw = new PrintWriter ( System . out ) ;
  int N = sc . ni ( ) ;
  int M = sc . ni ( ) ;
  boolean [ ] [ ] adj = new boolean [ N ] [ N ] ;
  for ( int i = 0 ;
  i < M ;
  i ++ ) {
    int a = sc . ni ( ) - 1 ;
    int b = sc . ni ( ) - 1 ;
    adj [ a ] [ b ] = true ;
    adj [ b ] [ a ] = true ;
  }
  char [ ] vals = new char [ N ] ;
  Arrays . fill ( vals , 'b' ) ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    for ( int j = i + 1 ;
    j < N ;
    j ++ ) {
      if ( ! adj [ i ] [ j ] ) {
        if ( vals [ i ] == 'a' ) {
          vals [ j ] = 'c' ;
        }
        else if ( vals [ i ] == 'c' ) {
          vals [ j ] = 'a' ;
        }
        else if ( vals [ j ] == 'a' ) {
          vals [ i ] = 'c' ;
        }
        else if ( vals [ j ] == 'c' ) {
          vals [ i ] = 'a' ;
        }
        else {
          vals [ i ] = 'a' ;
          vals [ j ] = 'c' ;
        }
      }
    }
  }
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    for ( int j = i + 1 ;
    j < N ;
    j ++ ) {
      int diff = Math . abs ( vals [ i ] - vals [ j ] ) ;
      if ( ( adj [ i ] [ j ] && diff == 2 ) || ( ! adj [ i ] [ j ] && diff <= 1 ) ) {
        pw . println ( "No" ) ;
        pw . close ( ) ;
        return ;
      }
    }
  }
  pw . println ( "Yes" ) ;
  for ( char c : vals ) pw . print ( c ) ;
  pw . close ( ) ;
}

public static void main ( String [ ] args ) { FastScanner sc = new FastScanner ( ) ; PrintWriter pw = new PrintWriter ( System . out ) ; int N = sc . ni ( ) ; int M = sc . ni ( ) ; boolean [ ] [ ] adj = new boolean [ N ] [ N ] ; for ( int i = 0 ; i < M ; i ++ ) { int a = sc . ni ( ) - 1 ; int b = sc . ni ( ) - 1 ; adj [ a ] [ b ] = true ; adj [ b ] [ a ] = true ; } char [ ] vals = new char [ N ] ; Arrays . fill ( vals , ' b ' ) ; for ( int i = 0 ; i < N ; i ++ ) { for ( int j = i + 1 ; j < N ; j ++ ) { if ( ! adj [ i ] [ j ] ) { if ( vals [ i ] == ' a ' ) { vals [ j ] = ' c ' ; } else if ( vals [ i ] == ' c ' ) { vals [ j ] = ' a ' ; } else if ( vals [ j ] == ' a ' ) { vals [ i ] = ' c ' ; } else if ( vals [ j ] == ' c ' ) { vals [ i ] = ' a ' ; } else { vals [ i ] = ' a ' ; vals [ j ] = ' c ' ; } } } } for ( int i = 0 ; i < N ; i ++ ) { for ( int j = i + 1 ; j < N ; j ++ ) { int diff = Math . abs ( vals [ i ] - vals [ j ] ) ; if ( ( adj [ i ] [ j ] && diff == 2 ) || ( ! adj [ i ] [ j ] && diff <= 1 ) ) { pw . println ( " No " ) ; pw . close ( ) ; return ; } } } pw . println ( " Yes " ) ; for ( char c : vals ) pw . print ( c ) ; pw . close ( ) ; }
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