NETWORKDAYS(start_date,end_date,holidays,weekend)
start_date: starting date serial value
end_date: ending date serial value
holidays: array of holidays
weekend: array of 0s and 1s, indicating whether a weekday (S, M, T, W, T, F, S) is on the weekend, defaults to {1,0,0,0,0,0,1}
NETWORKDAYS calculates the number of days from start_date to end_date skipping weekends and holidays in the process.
If an entry of weekend is non-zero, the corresponding weekday is not a work day.
This function is Excel compatible if the last argument is omitted.
This function is OpenFormula compatible.