x = input()
x = x.split(' ')
print(int(x[0])//2)25A - IQ test | 785A - Anton and Polyhedrons |
1542B - Plus and Multiply | 306A - Candies |
1651C - Fault-tolerant Network | 870A - Search for Pretty Integers |
1174A - Ehab Fails to Be Thanos | 1169A - Circle Metro |
780C - Andryusha and Colored Balloons | 1153A - Serval and Bus |
1487C - Minimum Ties | 1136A - Nastya Is Reading a Book |
1353B - Two Arrays And Swaps | 1490E - Accidental Victory |
1335A - Candies and Two Sisters | 96B - Lucky Numbers (easy) |
1151B - Dima and a Bad XOR | 1435B - A New Technique |
1633A - Div 7 | 268A - Games |
1062B - Math | 1294C - Product of Three Numbers |
749A - Bachgold Problem | 1486B - Eastern Exhibition |
1363A - Odd Selection | 131B - Opposites Attract |
490C - Hacking Cypher | 158B - Taxi |
41C - Email address | 1373D - Maximum Sum on Even Positions |