Put-call parity

For European calls and puts their prices are related by the Put-call parity:

$p + S_0e^{-qT} = c + Ke^{-rT}$

where $p$ and $c$ are the prices of the put, call options and $S$ is the current spot price of the underlying, $K$ the strike price, $T$ the time to maturity. The interest rate is integrated with $r$ and $q$ denotes the dividend yield on the stock.