Old money converter - £sd to decimal

In the old pounds, shillings and pence system, there were:

• 20 shillings in a pound
• 12 pence in a shilling
• 2 half pennies in a penny
• 4 farthings in a penny
• 2 farthings in a halfpenny

Input a value in pounds, shillings and pence to convert to decimal currency.