Service tax on foreign consultant

We have taken service from foreign engineer for 1000 Euro he raised bill for 1000 Euro & we booked bill in Feb17 @ 70 per EURO so bill amt in INR is 70000. we made payment in April for 1000 Euro @ 68 for Rs.68000. now i want to know as per service tax on foreign consulant we are liable to pay service tax, but i want to know on which amount. amt paid Rs.68000 or bill booked Rs.70000, pls advise me