What is the proportion of revenue from the IBW and ISM segment over total revenue in 2018?
{"(in thousands)": {"": 2019, "Fiscal Year Ended March 31, ": 2018, "Increase (Decrease)": 2019}, "IBW": {"": 12474, "Fiscal Year Ended March 31, ": 23265, "Increase (Decrease)": -10791}, "ISM": {"": 17263, "Fiscal Year Ended March 31, ": 19350, "Increase (Decrease)": -2087}, "CNS": {"": 13833, "Fiscal Year Ended March 31, ": 15962, "Increase (Decrease)": -2129}, "Consolidated revenue": {"": 43570, "Fiscal Year Ended March 31, ": 58577, "Increase (Decrease)": -15007}}
ibw_revenue = df["IBW"]["Fiscal Year Ended March 31, "]
ism_revenue = df["ISM"]["Fiscal Year Ended March 31, "]
total_revenue = df["Consolidated revenue"]["Fiscal Year Ended March 31, "]
answer = (ibw_revenue + ism_revenue) / total_revenue