How can I measure voltage in range -15 V to 50 V with an ADC in a microcontroller in a single circuit arrangement for scaling?

Possible Duplicate: How do I measure a negative voltage with a ADC? How do I sample a -2 V to +2 V analog signal with a PIC microcontroller?

I want to measure the negative and positive DC voltage with a microcontroller... If the voltage is not in the range of 0 to 5 then I will need some divider circuit or the scaling circuit to measure the voltage... In measuring positive voltage the voltage divider circuit is useful, but for measuring the negative voltage I need some circuit. What would be a scaling circuit which will scale -15 to 55 V to 0 to 5 V.