double Average( istream & fin )
     {
         int ItemsRead = 0;
         double Sum = 0.0;
         double X;
        
         while( fin >> X )
         {
             Sum += X;
             ItemsRead++;
         }

         return Sum / ItemsRead;   // Precondition guarantees ItemsRead!=0
     }

     int main( )
     {
         ifstream fin;

         fin.open( "input.txt" );
         cout << "Average is " << Average( fin ) << endl;

         return 0;
     }