The Garman Kohlhagen (1983) closed form currency option pricing model is defined as follows: 

OV = option value. S =current exchange rate. X = exercise rate (strike). r = domestic country's riskfree interest rate, expressed with continuous compounding. r_{f} = foreign country's riskfree interest rate, expressed with continuous compounding. vol = volatility of the relative price change of the underlying asset. T = time to maturity measured in years (actual/365 basis). N(.) = cumulative normal distribution of (.). iPC = 1 for call / 1 for put. 
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