x = input()
x = x.split(' ')
print(int(x[0])//2)555B - Case of Fugitive | 551A - GukiZ and Contest |
1399F - Yet Another Segments Subset | 1371C - A Cookie for You |
430B - Balls Game | 1263A - Sweet Problem |
1332B - Composite Coloring | 254A - Cards with Numbers |
215A - Bicycle Chain | 1288B - Yet Another Meme Problem |
1201C - Maximum Median | 435A - Queue on Bus Stop |
1409B - Minimum Product | 723B - Text Document Analysis |
1471C - Strange Birthday Party | 1199A - City Day |
1334A - Level Statistics | 67B - Restoration of the Permutation |
1734A - Select Three Sticks | 1734B - Bright Nice Brilliant |
357B - Flag Day | 937A - Olympiad |
1075A - The King's Race | 1734C - Removing Smallest Multiples |
1004C - Sonya and Robots | 922A - Cloning Toys |
817A - Treasure Hunt | 1136B - Nastya Is Playing Computer Games |
1388A - Captain Flint and Crew Recruitment | 592B - The Monster and the Squirrel |