The method should average six POSITIVE integers. Integers which are negative or zero should not be included in the average. If all the numbers are invalid return -1. Is there anyway to shorten this code?

```
public float averageSix( int a, int b, int c, int d, int e, int f ) {
 if( a < 0 ) { a = 0; }
 if( b < 0 ) { b = 0; }
 if( c < 0 ) { c = 0; }
 if( d < 0 ) { d = 0; }
 if( e < 0 ) { e = 0; }
 if( f < 0 ) { f = 0; }
  float aver = ( ( a + b + c + d + e + f ) / ( ( a / a ) + ( b / b ) 
   + ( c / c ) + ( d / d ) + ( e / e ) + ( f / f ) ) );
 if( aver = 0 ) { aver = -1; }
  return aver;
}

```