/////////////////////////////////////////
////   Wallet.java          
/////////////////////////////////////////
public class Wallet {
    private int tw, f;    

    public Wallet( ) {
        tw = 0;
        f = 0;
    }

    public Wallet (int tw0, int f0) {
        if (tw0 < 0 || f0 < 0 ) {
            throw new IllegalStateException(
                    "Illegal negative value:" 
                    + tw0 + " " +  f0 );
        }
        tw = tw0;
        f = f0;
    }

    public int value( ) {
        return (tw*20) + (f*5);
    }
    
    public boolean canChange( ) {
    	return (f >= 4);
    }

    public void minimizeWhile( ) {
    	while (canChange( )) {
    		f -= 4;
    		tw++;
    	}
    }
    
    public void minimize( ) {
    	tw += f/4;
    	f = f % 4;
    }

    public String toString( ) {
        return (tw + " 20s and  "
                + f + " 5s total "
                + value( ));
    }
}