using System;

public class Moyenne
{
  public static void Main()
  {
    int x = 0, n = 0, sum = 0;
    int[ ] tab = new int[ 100 ];

    try
    {
      string st = Console.ReadLine( );
      x = int.Parse( st );

      while ( x >= 0 )
      {
        tab[ n ] = x;
        n++;
        st = Console.ReadLine( );
        x = int.Parse( st );
      }
      int length = n;

      for ( int i = 0; i < length; i++ )
      {
        sum += tab[ i ];
      }
      float moy = (float)sum / length;
      Console.Out.WriteLine( "{0:N2}", moy );
    }

    catch ( Exception e )
    {
      Console.Out.WriteLine( "Entree invalide !" );
    }
  } // main()

} // class Moyenne