Usinging RF Reciever's output to Trigger a 555 one shot

I am trying to use the positive pluse output from a RF Reciever to trigger a 555 one shot circuit.

The 555 trigger input looks for a negative going pulse and is very sensitive.

How can i use the momentary 4volt output from the RF Reciever to generate a negative-going spike to trigger the 555 timer?

I was thinking of applying the circuit's input Voltage to the input trigger, and then somehow using the RF Reciever's 4volt output to pull down the input Voltage, therefore creating a negative-going spike.

Any easy and effective solutions to use the RF Reciever output to trigger the 555 timer?

Use a transistor (common emitter) to invert the pulse.